I saw it again and liked it much better the second time. However, I do think the scene at the end of the credits is beyond silly, one of those reversals that calls into question every single thing you've seen for three films.
Could have easily done without that little "twist."
i did go "whoa!" when I first saw it, but my overly geeky mind went into over time. Within the framework of the mutant universe, would Charles become just a man in that body. The mutant powers exist because of their genetics, their mutant dna. That means their power is bound to their particular body. When a mind transfer happens (assuming it could) Xavier's power would still be bound to his old body, wouldn't it? And would he still be Charles?
For me, I loved the philosophical questions that were explored in the comics, and enjoyed some of it in the first two. I felt like this last one, only touch on them without an real exploration. The idea of identity is import, but what happens when part of that identity is altered/suppressed. The "cure" has such a huge philosophic implication, and the film did nothing with that. For example, people who are bipolar struggle with the fact that taking medication suppress some of their mental acuity. They feel like they're in a fog all the time and don't feel like themselves. They feel like the medication takes away some of their identity. The "cure" in the X-men take that to a whole other level.
And the same question is also touched upon, with Jean/Pheonix. If Pheonix is a suppressed part of Jean, then is Jean also only a part of her whole, and not fully who she is? I would have loved to see Jean struggle with Pheonix more. I was hoping that like the comics, Jean finally does win out in that struggle, takes control of her body and her powers, but in an act of self sacrifice, destroys herself to prevent a cosmic disaster that Pheonix had started. I would have loved for her death to be more proactive and meaningful than it was.
