What I liked:
-The Score... one of my fav scores for an action movie (I own about 110 film scores). John Powell did a great job. I love the Pheonix Theme.
-The basic plot: I think "the cure plot" was an excellent way to continue the trilogy. But the cure plot + Dark Pheonix = total mess. They should of stuck to one or the other. "Magneto unleashes Dark Pheonix to destroy humanity" or "Mutants faced with taking a cure". One or the other. Not both. X-Men 3 was two movies in one, cut down to a measily 90 or so minute film.
-Beast, Kitty, Wolverine, Professor X, Magneto - the new characters of Beast, Kitty, plus the best actors/characters of the previous X-films... Wolverine, Professor X, Magneto ... continued to shine here. Did the X-Men films focus WAY TOO MUCH on Wolverine? Abso-freaking-lutely!!! But I think the X-Men trilogy really belongs to Hugh Jackman, Ian McKellen, Patrick Stewart.
-Magneto as reoccuring villain - I have mentioned before in many many other threads that although the X-trilogy is far, far, far from perfect (repeat: FAR from perfect)... the one thing it nailed wonderfully that I think other superhero films/directors-of-those-films should take notice to is it developed its main villain over three films and included side-villains in each sequel w/Magneto. That is a GREAT formula. Although most comicbook heroes have a large list of villains to use in each film, I think getting an actor to sign to play the MAIN VILLAIN in all three films of a trilogy, and developing that character slowly, just like the heroes, is a great idea. Imagine if Doctor Octopus had been introduced and developed a bit in Spiderman 1, then used in 2... or if Harvey Dent had been Rachel's boss in Batman Begins, then used in The Dark Knight... more character development, more impact....more emotional investment in the characters... only the X-Men Trilogy had the foresight to see its villain, Magneto, as a major player and developing character in each film. I think the whole "each film in the trilogy gets a new villain" idea is old/tired.
-I did like the development of the "kid" X-Men. ie Iceman, Collosus, etc.
-How Magneto was defeated - I like how he was defeated with trickery. Wolverine, throughout all three films, tries to fight Magneto, to no avail. He can't even challenge Magneto being that his body is made of a metal.... so I thought it was great how Magneto was beaten by tricking him into thinking Wolverine was gonna take him on... and then Beast creeps up behind and injects him in the back with the cure.