The X-Men franchise while is under Marvel, is not helm by the Marvel Studios, which also explains why my favourite Spider-Man is not in the Avengers! Franchise is currently out for loan to other studio who made X-Men not too bad except for the Last Stand where we all cried seeing the legacy of X-Men crumble in subpar plotted movie. While I shall not mention bout the visual of the show, nor about the the comic part of it, this X-Men portray a lot crossover from the past and present. With the lead cast all coming back and also the cast from First Class coming back to together. X-Men once again capture the attention of the audience.
TL;DR: past and presence timeline, lots of new and old mutants, sentinel threatning human and mutant race, x-men wins with some cost of the future.
P/s: just enjoy the movie. Don't question the storyline until the end. Stay back after credits for short scene and also to make your money's worth. Lol