First Class was pretty good, considering they used absolutely some of the lamest X-Men around. As someone who's seen every episode of the animated series, seen all the films, and casually kept up with the comics, even I had very little connection to the mutants they chose. (Outside of ones we've seen before and Emma, of course.)
The makeup on both Beast and Mystique were horrid. Horrid, horrid. Jennifer Lawrence was a terrible choice. Fuck canon, Kelsey Grammar was born to play Beast.
Charles and Erik? Superb. Even Kevin Bacon was good as the villain. But I cant even remember his characters name and I've seen the film a few times.
I will always love Bryan Singer. The very first scene of X-Men, the nazi camp scene, that's the first scene I can remember in any genre film, where I went, "Damn, that was powerful." It was powerful enough for Vaughn to re-use it in his movie too, I guess. It carried such weight; raw emotion. Then the scene that followed, seeing Patrick and Ian facing each other, that changed the game there, for every comic book fan everywhere.