Least of the trilogy - a few problems but still a strong showing Kowtowing to the wishes of Halle Berry has done significant damage. The movie was pretty much the Wolverine and Storm show because she demanded more to do as befits her station as an Oscar recipient. The problem is, she was given so much to do that short shrift was given to most of the other characters on team Xavier.
I begin with the film's weaknesses first, because there were several.
The plot had potential but fell short. The mutants you saw picketing the cure as well as the mutants lining up for it -- looked like normal people. There were few drastic mutations on anyone except Magneto's team. This made things look bad for Xavier's team, too, for that matter; Xavier's group is the one with the dream of unity between human and mutant, and his team had the "pretty" mutations.
The special effects were less than sensible. The scene wherein Magneto rescues Mystique does have the cool factor, but it falls flat because although Mystique, Madrox, and Juggernaut were all treated as "dangerous criminals", and the government acknowledged that capturing Mystique was inviting Magneto's wrath -- they had these prisoners in a convoy of _all metal vehicles._ It's only later in the movie when they're going "no metal, no metal."
Fans of the comic would spot discontinuities in the characters Magneto recruits.
It seemed this movie was built with "let's do fan favourites and show off how cool our special effects are, but barely attend to anything else" in mind first and foremost.
The Danger Room is only obvious for what it is if you're a comic reader. It's never identified, nor is the Sentinel Wolverine takes down. Likewise, neither is the Fastball Special move wherein Colossus throws Wolverine at an enemy.
Jean Grey as Phoenix without a Phoenix Effect is practically a slap in the face to a comic reader. Also, she's supposed to be as beautiful as she is terrible, but the effects used made her look psychotic, and like her powers were destroying her from the inside out.
Angel's part is small and not memorable. Leech's part likewise. The majority of the other mutants were just extras thrown in to be Magneto's army...
All that out of the way, what there is good about this movie is the characterization. Rock solid. Well portrayed for the most part.
Beginning with Sir Ian McKellan as Magneto: The man goes from being charming and campy in one scene to tragic in another, to cold and heartless, to astonishingly respectful, to briefly benevolent, and back to ruthless and vicious. His range is seemingly without limit, and every moment he's on the screen, he's captivating.
Rebecca Romijin has barely any screen time, but she does well with Mystique. Her acting for two movies and part of a third was mostly through airbrushed blue paint, contacts, and latex prosthetics, and she pulled that off. She was able to portray Mystique's adoring devotion to Magneto believably, and more, to portray her shattering sense of horrified betrayal when Magneto turns his back on her.
Paquin was a little overwrought as Rogue, but that's forgivable as her character is the one X-Man who might genuinely benefit from a cure.
Stewart was a little understated, still playing the kindly Xavier, even when his ethics were questionable. And that was chilling, really. He did things he wasn't sure weren't reprehensible himself, but with the conviction he was doing them for the best reasons. And Stewart made that visible.
Grammar as the Beast was the best bit of new casting for this movie. He had the intellectual, elegant, classy vibe completely down to an art.
Janssen as Phoenix/Jean was actually one of the best acted parts in the movie. Despite a horrible costuming job, an atrocious wig, and practically no lines at all, she portrayed the fight of good Jean Grey vs. chaotic Phoenix persona all the way through the movie. People who don't understand how Wolverine could get thrown around by her in one scene but he gets near to her in the end aren't noticing this subtlety of the performance...Jean loved Logan in her way, and was allowing him close enough to stop her while she still could.
Jackman as Wolverine pulled off the complexity of the most popular character. Again, people who thought that Wolverine's show of emotion was unseemly and out of character for him miss the subtlety of his performance, and the depth of character; Wolverine has always been more than animal senses and claws.
Berry as Storm is as she has been throughout the series -- consistently bad. Her scenes are either overacted or under-acted. The best scenes in which Storm appears are the ones that should've been in from the first two movies -- Storm using her powers. Any talented woman who took the role seriously could've done better. She has more to do, but thankfully, the special effects do most of the brilliance of the character here because Berry has never respected the role to do more than phone in her "performance."
This said, it's still a decent movie. It is clear that multiple script changes, directoral musical chairs, and the rushed script-to-release are why there are so many obvious flaws.
It's the weakest of the trilogy, but the darkness and characterization kind of outstrip the problems with script and direction. With any luck, the DVD will have deleted scenes that fill those in.
As a summer blockbuster goes, it's good. As an X-Men movie goes, it's so-so at best, especially in comparison with the first two. But so-so is still pretty entertaining.