For years in film, death was the end. Most actors usually did a project and then moved on. Now, things are different. Actors tied into franchises have opportunities to return in many different ways, whether it be in flashbacks or a full on resurrection.
The only problem is that sometimes bringing back these characters makes events from earlier films seem meaningless. While sometimes good writing can warrant the return of a character, other times the return isn't explained at all and the character is just thrown in for nostalgia and easy box office money. Sometimes it even comes at the expense of the characters themselves, and diminishes the excellent development or arc they had to begin with.
Harry Hart
The Kingsman franchise has really cemented itself as a fun action series with distinct fight choreography. The first film introduced the world and the titular spy agency. Many fans fell in love with Colin Firth as Harry Hart as he mentors Eggsy. His death in the climax came as a huge surprise to many and was genuinely heartbreaking to see.
Once the sequel came around, Colin Firth was already confirmed as part of the cast and the reveal that he survived was blatantly spoiled in the first trailer. While it would have been better to save the revelation for theaters, Hart should have stayed dead, as his death was the necessary event to drive Eggsy into the character he is. Dealing with that loss would have been a more interesting story thread to follow.
Agent Phil Coulson
Easily one of the best supporting MCU characters and a fan-favorite on Agents of S.H.I.E.L.D., Agent Phil Coulson's death in The Avengers came as a shock to many. His death is essentially becomes what The Avengers want to "avenge". With zero plans for the character to return in any MCU films, his death and return in Agents of S.H.I.E.L.D. in many ways feels a bit cheap.
While in the show his return is explained, no characters in the films are even aware of his status. While the show had some really great moments, the lack of connections with the wider MCU made it feel less important.
Imhotep
Stephen Sommers' 1999 reboot of The Mummy is just perfect. It's a great throwback to old adventure films with great action, suspense and romance. And one of the best parts of the movie was the titular villain Imhotep.
With not a single line in English, Arnold Vosloo still delivers an extremely menacing performance as the undead Mummy. Due to the success of the first film, a sequel was greenlit and Imhotep returns as the antagonist despite dying at the end of the original. While The Mummy Returns is still a ton of fun, it cheapens Imhotep and makes him less intimidating as the threat of the Scorpion King looms over.
Han Lue
Initially introduced as a one-off character in Tokyo Drift, Han would end up sticking around for quite a few films. Sung Kang's portrayal of character would make him go on to become a fan-favorite. Han is also just such a quotable character, offering lots of wisdom.
His death is properly explained in Fast & Furious 6 and it connects Tokyo Drift to the rest of the franchise in a really clever way. For the the 9th film, Sung Kang made his grand return to the character, but it's lazily explained that through hologram technology he faked his death. It feels unearned and makes the events of Furious 7 much less important.
Quaritch
There is so much excitement for Avatar: The Way of Water, a film nearly a decade and a half in the making. Many are already speculating it could be a major awards contender as well. Stephen Lang delivered a really good performance in the original, but almost 15 years later, is there really a reason to have the character return?
Despite meeting a grim end in the first film, Quaritch miraculously appears in the trailer for the sequel, but this time as a Na'vi. This revelation certainly raises a lot of questions, but unfortunately moviegoers will have to wait until December to find out.
Jason Voorhees
Best known as one of the most iconic horror movie villains, Jason Voorhees has died in nearly every Friday the 13th film from the beginning. Although the films in the series are fun to watch, they really don't hold any stakes whatsoever, as Jason will just be resurrected in the next film.
Jason would work a lot better just as an undead supernatural being rather than a convoluted external force always bring him back to dead. It's wild that a Friday the 13th film hasn't been made in 13 years, as there's a lot of things that can be done to revitalize it.
Steve Trevor
Steve Trevor's return in Wonder Woman 1984 was quite possibly one of the worst things in the film, especially in the manner it's done. Trevor is resurrected through the Dreamstone but in the body of another man. This opens up the story to a lot of weird twists.
Towards the finale, it's gut-wrenching seeing Diana have to give up Steve once again, but in all honesty, the character should have stayed dead, allowing Diana to further grow without him.
Gamora
Gamora's fate at the hands of Thanos was one of the most unexpected and emotional scenes in Avengers: Infinity War. The stakes were higher than ever during that film and with Loki's death and the snap that killed half of the Avengers, many were terrified as to who would make it in Endgame.
Once Endgame undid all the deaths from the Snap and brought back past versions of Gamora and Loki, the stakes were low once again. Having a past version of Gamora completely negates all the character development she went through with the Guardians. It's a shame. Having her stay completely dead would have set up a really interesting dynamic for the Guardians. Fans continue to theorize Gamora's whereabouts, but hopefully all will be revealed in Guardians of the Galaxy Vol. 3.
Neo
Although The Matrix Revolutions has many flaws, it still delivered an epic yet satisfying conclusion to The Matrix series. With Neo and Trinity both dying, many were confused once it was revealed they'd both be returning for Resurrections.
The explanation for both of their returns is really sloppy, and by the end of the film, it completely backtracks on Neo being the One, with it being Trinity instead. Films that retroactively change events of previous films usually don't go over well with audience. While it was cool to return to the world of The Matrix, many fans were left disappointed.
Emperor Palpatine
Emperor Palpatine is quite possibly one of the most iconic villains in cinema history. He is recognizable even by non Star Wars fans. While the reveal of his return was met with a lot of excitement, his return was very poorly executed.
There are very few indications for how his resurrection occurred in The Rise of Skywalker, other than passing lines of dialogue mentioning cloning, dark magic and the most memed line ever, "Somehow Palpatine returned". It's unfortunate the finale of the Skywalker Saga ended on a low note, as the film completely undermines Anakin bringing balance to the force and what George Lucas created before.