The Marvel Cinematic Universe has been filled with moments that took fans' breaths away. From Nick Fury breaking into Tony Stark's house in the middle of the night (because that's totally what he did) in Iron Man, to the titular heroes standing together amidst the Chitauri invasion in The Avengers, to that 360-shot of the entire team protecting the drill in Avengers: Age of Ultron (including Captain America's awesome, though completely unnecessary, twisting somersault to take out one of Ultron's drones). The list of great moments goes on and on.

Though the MCU has been filled with greatness, not everything has been gravy. There have been quite a few cringe-inducing moments that we'd like to forget, and many others that for some reason or another simply missed the mark. These are the moments that could have (and should have) forced our heads to explode out of sheer joy, but ended up falling flat -- or worse, not happening at all. Instead of going down as some of the greatest MCU moments to date, these will be forever remembered with a sliver of sadness for what could have been.

Here are the MCU's 15 Biggest Missed Opportunities So Far.

Honorable Mention: linking the movies to the Netflix series. The Netflix series are filled with subtle nods toward the films, but the films don't have any nods back. It wouldn't kill the MCU to have a few newspapers with articles dedicated to the "Devil of Hell's Kitchen" lying around. This missed opportunity doesn't make the list, however, because not all fans of the films watch the television series, so any such nods would go unnoticed by a chunk of the fan base anyway.

15. keeping surprises secret

Hulk catching Iron Man in Avengers

We start with a macro example that seems to be plaguing the film industry as a whole, and that is the sheer lack of surprises. Between behind-the-scenes images and videos showing up on social media (like this one) and actors being spotted on the sets of movies where their involvement up until that point was mostly kept secret, spoilers abound and genuine surprises are growing increasingly infrequent.

Granted, much of this is our fault, because many of us are MCU-obsessed and sometimes seek out this information online. Some spoilers, however, fall completely at the feet of Marvel itself. Take the Hulk catching Iron Man at the end of The Avengers, for example. The impact of this epic moment in which Bruce Banner manages to control his alter ego long enough to catch his falling friend was lessened by the fact that Marvel spoiled it in the trailer. A more recent example is Iron Man showing up to help Spider-Man save the sinking ferry in the second Homecoming trailer. The intrigue stirred up by the first trailer's final image of Spidey struggling to hold together the massive ship is undone the moment Tony arrives in trailer two.

14. bruce's control of the hulk

Bruce Banner green eyes The Avengers

Bruce Banner's ability to control the not-so-jolly green giant has been fluctuating ever since MCU movie number two. Bruce struggles with the big guy for much of The Incredible Hulk before seemingly taking control by the film's end. Then Banner shows up again in The Avengers and (for some unexplained reason) no longer has control, but somehow regains some degree of it for the battle of New York. Then he returns in Age of Ultron, where he sort of has control thanks to Black Widow's lullaby, but according to the trailer for Thor: Ragnarok, he seems to once again be out of his mind.

Banner's inability and then ability to control the Hulk has been a source of confusion for years now, which is a shame considering how easy it would have been for Marvel to nip it in the bud on day one. Rather than ending The Incredible Hulk with Edward Norton smirking at the camera, seemingly in command of the big green monster, all Marvel had to do was shoot a more ambiguous ending. Put Banner in a situation where he could potentially lose control and cut to black before he does, leaving the audience in suspense and making the first half of The Avengers much less confusing.

13. vision's loyalties

Vision frowning in the woods in Avengers: Age of Ultron

Let's get this out of the way: Vision lifting Thor's hammer while the rest of the Avengers look on in stunned disbelief was not only one of the highlights of Age of Ultron, but one of the funniest MCU moments to date. That being said, it also robbed the film of one of its more intriguing plot threads by having Vision gain the Avengers' trust just moments after his birth. Vision was literally created by Ultron and at one point flat out admits, "maybe I am a monster. I don't think I'd know if I were one." Without Mjolnir, the Avengers would have been forced to fight alongside a potential monster in order to defeat Ultron. This would have made the final battle much more compelling, with each Avenger forced to keep an eye on Vision throughout.

This also could have saved the crowd-pleasing moment for the film's climax. Picture this: Ultron has Thor by the throat and we get a quick shot of Mjolnir sitting on the ground with Ultron and Thor in the distance. Then Mjolnir is lifted by an unseen figure and Ultron is whacked out of frame revealing Vision holding the hammer. This would finally show where Vision's loyalties lie while delivering an epic MCU moment, as opposed to just a funny one.

12. Quicksilver's train rescue scene

Aaron Taylor-Johnson as Quicksilver in Avengers: Age of Ultron

Quicksilver had quite the calendar year on film from May 2014 to May 2015. He appeared in both X-Men: Days of Future Past (played by Evan Peters) and Avengers: Age of Ultron (played by Aaron Taylor-Johnson), stealing the show in the former and being a bit of a bore in the latter. What made his appearance in Age of Ultron so disappointing (aside from the fact that Days of the Future Past had already knocked the character out of the park) was that he didn't get a chance to shine.

The perfect opportunity to showcase Quicksilver's skills was during the runaway train sequence when he pulls people out of the train's path. In the scene, Quicksilver is mostly a blur as he goes about saving just five people. Five! It amounts to a complete waste of the character, as so much more could have been done. Slow motion shots of him pulling groups of innocent bystanders out of the way just moments before the train barrels through them would have been much more interesting to see on screen. The sequence may not have been as good as DoFP, but it would have been much better than what we got.

11. Few crossovers in phase 2

Iron Man 3 Robert Downey Jr Suit

Fans waited years for Earth's Mightiest Heroes to finally appear on screen together in 2012's The Avengers. Four years to be exact, and the wait was worth every minute to finally see Earth Mightiest Heroes fighting side by side. Then they went their separate ways at the film's end and mostly stayed that way until Age of Ultron. This was a huge missed opportunity for Marvel, and one the studio seems hellbent on correcting in Phase 3 (as evidenced by virtually everyone appearing in Captain America: Civil War, Tony Stark set to appear in Spider-Man, and Hulk showing up in Ragnarok).

Phase 2, however, could have been so much more fun than it was. How about having Bruce Banner show up in Iron Man 3 (in more than just a cameo) to help Tony fight off the Mandarin? Or Thor recruiting one of his fellow Avengers (since he did come to Earth, after all) and to help fight Malekith, who was on the brink of destroying all of existence? There were countless opportunities for crossovers throughout Phase 2, and Marvel ignored every single one of them for the most part.

10. bruce and natasha's relationship

Bruce Banner and Natasha Romanoff look concerned in Avengers Age of Ultron

Speaking of Phase 2 crossovers, two characters whose relationship would have greatly benefited from more time on screen together are Bruce and Natasha. He went from practically killing her in The Avengers to dating her in Age of Ultron. And the last time we saw her on screen, she was making out with Steve in Captain America: The Winter Soldier. This made it a bit jarring when the Hulk and Black Widow were suddenly in a relationship the following year.

Marvel would have been better off using previous films to hint at the budding relationship. This would have been a bit difficult, considering the two only appeared alongside each other in The Avengers, but that just goes to show that the studio should have produced more crossovers in Phase 2. Having both characters appear in one of the Iron Man, Thor, or Captain America sequels would have given their relationship more time to develop, and it would have made Bruce's decision to leave Natasha at the end of Age of Ultron all the more powerful and heartbreaking.

9. relationships in general

Thor and Jane Foster

The relationships thus far featured in the MCU have left a lot to be desired. Betty Ross and Bruce Banner seemed destined to be together, and then The Incredible Hulk ended and we haven't seen her since. Jane Foster made it through two Thor films, but will not appear in Ragnarok, so that looks like the end of her relationship with the God of Thunder. And even Pepper and Tony's involvement, which was given time to blossom over the course of four films, including The Avengers, seems to have come to an end. She was barely mentioned in Age of Ultron, and it was heavily implied that the two are all but done during the events of Civil War though this (could soon change).

It's unfortunate that in a series that is now 14 films strong, there is not one relationship seemingly built to last -- or at least one worth investing in. The only one to receive some proper closure so far is the relationship between Steve and Peggy Carter, which came to an end when the latter passed away in Civil War. And even then, Steve almost immediately started making out with her great niece, Sharon. (Damn it, Steve!) Not all of these relationships need to last for the entire series of films, but Marvel had many opportunities to bring closure to them in one form or another and opted instead to have characters simply vanish without a trace.

8. ultron

Ultron from Avengers and Marvel Comics

Think back to the first trailer for Avengers: Age of Ultron. You know the one. It starts with a deliciously wicked Ultron voiceover in which he declares, "I want to show you something beautiful. Everyone screaming...for mercy." This line combined with the melancholic music and imagery (not to mention that cover of "I've Got No Strings" that just gets under your skin) painted the film as having a dark tone, unlike any MCU film to come before it. It was an interesting, and welcomed, new direction for the MCU after ten films that generally shared the same light-hearted feel.

Then the film hit theaters, where fans learned that it was much closer in tone to The Avengers than the original trailer suggested. The biggest missed opportunity, however, came in the form of Ultron himself, who was not nearly as menacing as he could have been. Instead, the character was mostly played for laughs (at one point forgetting the word "children" and even saying, "oh for God's sake" just before being thrown out of a jet by Hulk). Even if the studio wanted the rest of the film to feel like its predecessors, Ultron could have been much darker and scarier than the version we received, and the film would have been better for it.

7. killing hawkeye

Hawkeye Family in Avengers Age of Ultron

Speaking of Age of Ultron, another huge missed opportunity came when Marvel decided to kill off Quicksilver rather than Hawkeye. Now, some will argue that Hawkeye's death would have been telegraphed -- especially considering he is arguably the most disposable Avenger, and the writing was all over the damn wall after the film suddenly introduced his wife and kids -- but that doesn't change the fact that he should have been the one to meet his maker by the film's end.

That's not to say Hawkeye isn't an interesting character; it's just that his death would have had a greater impact on the MCU as a whole. The Avengers, and fans themselves, formed a much stronger bond with Hawkeye than they ever did with Quicksilver. In fact, the only person affected by the latter's death is Scarlet Witch, and even she seems over it by Civil War. Hawkeye's death, however, would have cut the team to its core, given stakes to future films (where central Avengers would no longer feel untouchable), and saved Quicksilver for Civil War. Admit it, Quicksilver would have made for much more interesting fight sequences than Hawkeye.

6. the mandarin

The Mandarin on his throne in a promo image for Iron Man 3.

The Mandarin would have ranked higher on this list had Marvel's decision to make the character a joke (at least for the time being) not already been raked over the coals by critics and general audiences alike. Iron Man 3 is the second best Iron Man movie to date, but it could have been so much more. Ben Kingsley's version of the Mandarin had the potential to be legendary. He was cold, calculating, seemed completely capable of bringing Tony Stark to his knees, and his delivery of the line, "you'll never see me coming" was absolutely chilling.

Then it was revealed that Kingsley's character was an actor posing as the international terrorist, and the film quickly pivoted to Aldrich Killian as the main antagonist. The revelation made for a good laugh and a genuine shock, but it ultimately sacrificed what could have been an epic showdown pitting Tony's Iron Man suit against the powers of the ten rings (however Marvel chose to showcase them). Hopefully, the true Mandarin hinted at in "All Hail the King" will make an appearance in the future and help rectify this misstep.

5. pulling punches in civil war

Captain America Civil War - Iron Man and War Machine

The airport battle depicted in Captain America: Civil War was one of the greatest action sequences ever put to film. That being said, Marvel missed the opportunity to make it even better by raising the stakes. The fact of the matter is the "war" implied by the film's title wasn't a war at all. Instead, it was a six-on-six game of "capture the Bucky" with the heroes pulling their punches throughout (with the exception of Black Panther, who totally wanted to murder Bucky). The only real injury comes when Vision accidentally blows War Machine (who was on his own team, by the way) out of the sky.

The entire film hinges on the airport sequence, and the lack of stakes hurts it overall. In fact, the chase sequence between Black Panther, Bucky, and Cap, as well as the end fight between Bucky, Cap, and Iron Man, hold much more weight because the stakes are raised. T'Challa and Tony are trying to kill Bucky, and Bucky and Cap are doing everything they can to stop them. The airport battle needed more of the same. Raising the stakes via some personal loss (even if this means killing a character earlier in the film or in the battle itself) would have heightened emotions and made for a more compelling battle.

4. Avengers 2.5

Captain America: Civil War - no alternate endings filmed

Of all the MCU's solo films, Captain America's were shaping up to be the best. Hulk's stopped after Incredible, and none of the Thor and Iron Man sequels didn't live up to their original tales. Captain America: The First Avenger, however, took a dated character who debuted in 1941 and not only made him relevant, but cool. Then Captain America: The Winter Soldier improved on the original in nearly every way on its way to becoming one of the MCU's best films to date. This left fans wondering where the series would go in its third entry.

Marvel's announcement that Captain America 3 would be subtitled Civil War caused a frenzy with fans of the famous comic who wanted to see it brought to life on the big screen, but did so at the expense of Cap's third solo film. In its place essentially came Avengers 2.5, which turned out to be a watered-down version of the comic that didn't progress many character arcs set up in the previous films. Civil War was undoubtedly an entertaining movie, but there was no need for it to be a Captain America film. Marvel would have been better off concluding the Captain America trilogy and providing some form of closure for the character (like they did with Tony in Iron Man 3), and then producing Civil War as its own standalone film somewhere down the line.

3. glossing over tony's retirement

Tony Stark's vision as he looks heartbroken in Age of Ultron

Speaking of Tony's closure, despite Marvel's decision to make the Mandarin a bit of a joke, Iron Man 3 was a good movie. Tony and Pepper's relationship continued to evolve, we got to see how the battle of New York affected Tony's personal life, and he seemingly decided to give up being Iron Man (hence him destroying his suits, having the arc reactor surgically removed from his chest, and throwing said arc reactor into the ocean). It was a welcomed departure from the expected, since fans knew Tony would appear in Age of Ultron and were curious to see how him giving up being Iron Man would affect the film.

Then the opening scene in Age of Ultron had the Avengers raiding a HYDRA base, and Tony was right back in his Iron Man suit...as if the events of his last film never happened. It was a real head-scratcher. Why have Tony destroy his suits, remove the arc reactor, and throw it away if the plan was to put him right back in the suit in the next entry? Instead, Marvel had the opportunity to have Tony's character continue to evolve by having him do something (literally anything) else. He should have been building the Iron Legion or developing the A.I. for Ultron. Then tragedy (Hawkeye's death, perhaps?) should have forced him to dawn the suit once more, even though he thought he had finally moved on. It would have added another layer to Tony's character and kept the continuity of his films intact.

2. tony and steve's friendship

Chris Evans and Robert Downey Jr. as Steve Rogers/Captain America and Tony Stark/Iron Man looking sideways in The Avengers

The first trailer for Captain America: Civil War had fans practically salivating at the thought of seeing their favorite heroes duking it out in an all-out war. The emotional peak of the trailer comes when Steve proclaims, “I’m sorry, Tony. You know I wouldn’t do this if I had any other choice. But he’s my friend.” To which Tony replies, “So was I.” Then he, Steve, and Bucky beat the living crap out of each other. Downey’s delivery of the line (which was actually different in the film itself) was simply perfect, and made the fight between the two heart-wrenching.

In hindsight, this was a bit of a cheat, since the two never had much of a friendship to begin with. Their relationship in The Avengers was adversarial at best (with the two nearly coming to blows on the helicarrier before Hawkeye helped Loki escape), and their ideological differences were on full display in Age of Ultron. The two weren't exactly pals. In fact, they always seemed annoyed with one another whenever they shared a scene. While Marvel does receive points for planting the seeds of conflict early on, they lose some for not building a stronger friendship between the two. A stronger friendship (like the ones developed between Tony and Rhodey, or Tony and Bruce, or Steve and Sam) would have given the events of Civil War more weight.

1. not making a black widow solo movie

Scarlett Johansson as Black Widow

It's been seven years since Scarlett Johansson's Natasha Romanoff, aka Black Widow, debuted in the MCU, and fans are still clamoring for her to get her own solo film. The fact that she doesn't have one is a travesty, and by far the MCU's biggest missed opportunity so far. Instead of introducing the character in Iron Man 2 (one of the MCU's weakest entries to date), Marvel should have given Black Widow her own Phase 1 film just like they did with every other member of the Avengers not named Hawkeye. We would have even settled for an introductory team-up between the two longtime colleagues.

Johansson proved she can carry a movie on her own (not to mention crush the worldwide box office) with 2014's Lucy. Plus, her hand-to-hand fight sequences have been some of the best boasted by the MCU, and she is easily one of the most interesting characters to debut so far. A solo film about her past leading up to her joining S.H.I.E.L.D., or one based in the present about her life as an agent in a world where superheroes are popping up left and right, had the potential to be awesome. Instead, we received an Iron Man sequel that hit most of the same beats as the original and ultimately felt like a disappointment. Marvel can still produce the film at some point in the future, but until then a solo Black Widow movie remains the MCU's biggest missed opportunity to date.

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What other MCU moments can you think of that missed the mark or just fell flat? Let us know in the comments . And if you think you know everything about the MCU, take our quiz and put your knowledge to the test.