It turns out that one of the most difficult things to do is to have the final leg in a trilogy of films be the best installment. There have been some great third entries like Return of the Jedi, War for the Planet of the Apes, and How to Train Your Dragon: Hidden World, but they weren't the high points of their respective series.
With that being said, it is hard to find trilogies where the final movie is the best when it comes to the ratings on IMDb. However, that's the case with each of these impressive movie franchises.
Descendants 3 (6.6)
It's not often that made-for-television movies will appear on a list like this. However, Descendants turned out to be successful enough to spawn an entire franchise. The concept is a unique one, focusing on the lives of the teenage children of some of Disney's most famous villains. That includes the Evil Queen, Jafar, Cruella de Vil, and Maleficent.
The first two entries (6.4 and 6.5) were solid and the same could be said for the third, though it slightly scored higher. 2019's Descendants 3 sees the main characters visit the Isle of the Lost to recruit new villains. This was an emotional watch due to the tragic passing of young star Cameron Boyce about a month before it premiered.
Star Wars: Episode III - Revenge Of The Sith (7.5)
The Skywalker Saga is interesting because each of the three trilogies has appeared on lists like this. With the sequel trilogy, the first entry, The Force Awakens, scored above the rest. In the original three, the middle film, The Empire Strikes Back, was the best. However, the prequels ended on the highest note.
2005's Revenge of the Sith wrapped up the story that began with The Phantom Menace and Attack of the Clones (both 6.5) in great fashion. Anakin Skywalker completed his turn into Darth Vader, which included a fight with Obi-Wan that fans still argue is the best lightsaber battle of them all.
Captain America: Civil War (7.8)
It is widely agreed upon that the best trilogy within the Marvel Cinematic Universe so far belongs to Captain America. The First Avenger (6.9) was solid, while The Winter Soldier (7.7) is still held in high esteem as possibly the best solo entry of them all. In 2016, the trilogy ended with Civil War.
Although this can at times feel almost like an Avengers movie since so many heroes are featured (including with the debut of Spider-Man and Black Panther), the heart of it is the bond between Steve Rogers and Bucky Barnes. That rings true through all three movies and helps give this big action movie an emotional core.
Thor: Ragnarok (7.9)
Thor was the third MCU character to get a trilogy and a lot of audiences were unsure about it. After all, Thor (7.0) and Thor: The Dark World (6.9) aren't exactly considered all-time greats. However, director Taika Waititi took over and ensured 2017's Thor: Ragnarok would easily be the best.
Waititi injected a dose of humor, color, and creativity into this, allowing his actors to express their comedic chops. The whole thing made for a blast of an adventure. Thor teamed up with Hulk, Loki, and Valkyrie to stop his sister Hela from destroying Asgard. Sure, there's another installment coming but for now, this was the end of the trilogy.
The Bourne Ultimatum (8.0)
Speaking of franchises that went past three movies, there's the one centering on Jason Bourne. However, Jeremy Renner entered the series for the fourth installment and though Matt Damon returned after, many fans still view the original three as its own trilogy.
The Bourne Identity (7.9) and The Bourne Supremacy (7.7) were both well-received but they saved their best effort for last. 2007's The Bourne Ultimatum continues to follow Jason as he tracked down the origins of his own life while becoming the target of a similar program within the CIA. The spy drama and breathtaking action were all praised.
Three Colours: Red (8.1)
Although it's the least widely known set of movies on this list, there aren't many that are consistently met with as much praise as the Three Colours trilogy. It began with Three Colours: Blue (7.9) in 1993, followed by Three Colours: White (7.6) the next year.
Also in 1994 came the final entry, Three Colours: Red. This iteration continued the trend of utilizing the colors in the title throughout. Meanwhile, the plot centers on a model who forms a bond with the retired judge she lives next to who spends his time spying on people.
Logan (8.1)
Almost nobody saw this being as great as it was. Regardless of how perfect Hugh Jackman has been as Wolverine over the years, his first solo film, X-Men Origins: Wolverine (6.6) was met with poor reviews. The Wolverine (6.7) was more liked but still not an all-time great superhero flick. The trilogy following the mutant became truly special with 2017's Logan.
Taking story elements from the famed Old Man Logan comic series, this installment focuses on an elderly Wolverine at a time when mutants are nearly extinct. He goes on his final mission, which is to save a young girl with mutant abilities similar to his own. It is viewed as one of the greatest superhero films ever made now and was nominated for an Academy Award.
The Good, The Bad, And The Ugly (8.8)
There's a reason Clint Eastwood is held in such high regard by almost every film viewer. A major one is the "Dollars Trilogy," which began with A Fistful of Dollars (8.0) and continued on with For a Few Dollars More (8.2), both of which are considered among the best westerns ever made.
With the release of 1966's The Good, the Bad, and the Ugly, this series truly became something iconic. The plot sees three gunslingers competing to find a fortune but was really beloved for Eastwood's performance and the directorial style of Sergio Leone which included epic gunfights and impressive cinematography.
The Lord Of The Rings: The Return Of The King (8.9)
Although the word "epic" is tossed around often, it's incredibly fitting for The Lord of the Rings. Each film is grand in scale and was Oscar-nominated. The Fellowship of the Ring (8.8) sets everything up in intriguing fashion, while The Two Towers (8.7) delivers the biggest battle ever put on the big screen to that point.
When it came time for the series to conclude in 2003, The Return of the King was a true juggernaut. It set an Academy Award record for the highest clean sweep, winning all 11 categories it was nominated for, including Best Picture. The story of Frodo getting the One Ring to Mount Doom while the World of Men battled Sauron's army made for one of the greatest conclusions in history.