I'd have to go with - great plot, uneven characterization.
Loved the tone, and it was definitely *clever*.
Missing a few key elements for me -
Angel's defection - didn't care.
Raven's defection - didn't work. Not invested enough. The Beast/Magneto/Raven triangle didn't have enough of a hook. Her hurt when Hank decides to take the "cure" nearly played out, but not quite. I never really bought her throwing herself at Eric.
Magneto's arc was nearly just right, but something bothered me. Eric's whole point, the reason you can cheer for him is, he's been persecuted by *humans* his whole life. If now he's just after the mutant who killed his mother... well, doesn't it undercut the character? When Eric tells Sebastian "I agree with everything you've said..." I realized why I wasn't buying this.
Sebastian's death, linked to Charles, was brilliantly done. Erik's speech just after was abrupt and odd.
I thought Charles/Erik needed more push and pull. More moments of respect for each other, more moments of realizing this was not going to work. The tone was there, but not the meat. I wanted a few more moments where they each saw the right in what the other was doing.
Worth seeing, but a little frustrating in what was missing.