Warning: If you haven't seen the movie yet, you might not want to read what follows, because it will give away substantial portions of the plot. By the way, if you haven't seen it, be sure to stick around to see what happens at the end of the credits.
What a strange movie. I can understand why the reviews have been so mixed - it reflects the odd blend of quality in the film itself.
The premise is quite interesting; in the third installment of the X-Men films, the government has created a cure for the mutant gene. Magneto is certain that they will soon use it to eradicate the mutants, and wages war. The somewhat hapless X-Men are opposed to war, and thus, fight Magneto. What makes this tricky is that Magneto's concerns seem totally valid - despite the government's claims to only offer the cure to mutants who want it, within 20 minutes, they're firing syringe-loads at Mystique. But it gets more interesting still: when Hank McCoy, who is some kind of political representative of the mutants, discusses this issue with the president, portraying it as a threat to democracy, the president's response is that he fears for the state of democracy in a world where one man has the power to vaporize a city. This point is excellently borne out by Phoenix, the resurrected Jean Gray, who has a devastating amount of power, and no ability, or real willingness, to control it. Her character is bit sketchy - at times pure id, at times tormented Jean Gray, her motives are sort of puzzling, and for most of the movie, she just glowers in a corner. That's when she's not haunting people's thoughts, or getting pissed off and unleashing the apocalypse. In any case, as I said, the premise of the film is interesting, and skillfully handled. It's not an obvious good guys/bad guys split, it's actually quite nuanced. One has the sense that it's an allegory, but it's not a heavy handed one. You can't set up obvious parallels, like "mutants equal terrorists", or anything like that. Rather, the film stages the problems of multiculturalism and power imbalances, and provides a space for reflection.
However, while the plot is somewhat elegant and interesting, the dialogue is hamfisted, and the acting is awful. I was really puzzled by the fact that I was really irritated by the corny jokes in the movie. As I said in my review of The Transporter 2, below: "The real secret to an entertaining action movie, after great action, of course, is puns. Great puns." So why did the ones in this movie irritate me so much? My friend Russ, I think, figured out the answer. Puns, or corny jokes of that kind, are best used in a situation where there are some comic undertones, and with a kind of wink and smirk to the audience. They need to be somewhat ironic, even if not explicitly so. Also, I think, they should be a moment where you laugh/groan with the character, not at him. For instance, in Commando, when Arnold is asked what happened to a dude whom he droppedoff a cliff, he says "I had to let him go". That works. It's hilarious, and great, and Arnold knows it. In contrast, when Wolverine and Cyclops are arguing, and Cyclops storms down the hall, then pauses, and says "Not everybody heals as quickly as you do Wolverine", and then flounces off, it doesn't work. Cyclops seems totally oblivious to the cheese-factor of the line, as does Wolverine. The situation isn't a humorous one; the line just serves to add inappropriate humor to a melodramatic context, which prevents you from getting absorbed in the melodrama, making you realize how cheesy the whole scene is. Even when Charles says "You of all people, Storm, should realize how quickly the weather can change" - he kind of smirks, but it's a serious scene - the comedy is totally inappropriate.
This was the main weakness - shitty dialogue, and generally poor acting. The script was melodramatic and flat, and the actors, it seemed, couldn't decide whether to play it campy, seriously, or what, and ended up just kind of hanging out, occasionally acting distraught.
The movie certainly set itself up for an X-Men 4. I wonder if it'll be better, or worse.