I felt like the movie was enjoyable, but forgettable, because it’s a rehash of previous character stories we’ve already seen. Every X-Men movie has been an exploration of the theme “It’s better to respond to oppression with the high road of appeals to tolerance, rather than through violence against the class that your oppressors come from.”
But at least there was a new external plot. Unlike a lot of superhero sequels that don’t bother with a complete plot at all and just throw increasing numbers of super-villains at the hero. That type of movie always ends up being an incoherent mess. See Spider-Man 3, Amazing Spider-Man 2, Batman Returns/Forever/and Robin, etc. (Or don’t see them, since they’re terrible.)
After I saw the movie, I went back and re-read the comics it’s based on. I do feel like the movie improved on the comics, and had a lot more meat to it. But then 2 hours of movie necessarily contains a lot more stuff than 40 pages of comic book.
The theme of “It’s better to fight for civil rights through appealing to tolerance and compassion rather than through tribalist violence” is the entire point of the X-Men. It’s as central to their existence as “With great power comes great responsibility” is to Spider-Man or “Truth, justice, and the American way” is to Superman.
But comics are a different medium than movies. They’re an ongoing story with no clear end. What works in comics doesn’t necessarily work in movies, and the emotional emptiness of rehashing the same theme in multiple movies is a clear example of this.
One other side-note. Rereading the comics from 1980 reminded me of how ridiculous it was that Magneto and Mystique’s group refered to themselves as “The Brotherhood of Evil Mutants.” Nobody believes they’re evil. The movies (including Days of Future Past) improved on the comics by jettisoning this cartoonish point of view, and giving the villains real reasons for believing that they’re doing the right thing.