How the movie handles these errs slightly on the side of contrived, especially #3. The original canon has a mutant named Lucifer crushing Xavier’s back with a boulder; here, it’s Magneto’s fault (albeit indirectly) that Xavier becomes crippled. While Magneto’s remorse is a little cheesy, I found it a much more fitting moment, probably the best creative decision in the movie.
Personally, I would have liked to see some of these developments spread out over another prequel movie; to cram them all in at the end of First Class lessens some of the emotional impact, especially Mystique’s betrayal.
The jokes that don’t have a punchline are pretty interesting, too. I kept wondering to myself, Why does Alex Summers’ (Lucas Till) name sound so familiar? Turns out I was thinking of a mutant I met in 2000′s X-Men: Scott Summers, or Cyclops. In the comics, Alex Summers (a.k.a. Havok) is Cyclops’ younger brother, but First Class producer Bryan Singer — who came up with the stories for X-Men, X2, and First Class — decided that that wouldn’t fit this movie’s timeline. After all, Havok is a teenager in the movie’s setting of 1962, and Cyclops is in his late 20s in 2000 (if you’re assuming that’s when X-Men is set).
There are other details, including Xavier’s relationship to Rose Byrne‘s CIA agent Moira MacTaggert, that differ from the comic books’ continuity. These are more annoying than fun, but they’re nothing if not authentic: The comic book world is filled with these retroactive continuities (or retcons) that constantly twist history and canon to fit the latest adventure.