Since all of you seem so upset about it, I will justify Magneto's flightyness. Seriously, it isn't terribly out of character considering (SPOILER) he has been in solitary confinement underneath the Pentagon for likely 10 years. The dude isn't going to be right in the head after that.
Seriously.
And Mystique's thing, I totally get. Her whole big thing in First Class was that she didn't want to hide who she was. She is more comfortable being blue her and only is in disguise when necessary. (SPOILER) When reading about the sentinels and how they were going to kill mutants, I'm sure she was overwhelmed with emotion and more comfortable as herself.
In other news.
I enjoyed this movie so much. Much much enjoyment. Also stoked for Apocalypse to come.