Compared to what the movie SHOULD have been, it was horrible. Compared to the usual garbage that flows out of Hollywood, it was decent. The cinematography was moderate, the effects were laid on thick and the wrong things were focused on.
Warning, some spoilers below:
I agree with Spuds on the point of Magneto. The only thing they did right about him was what he said about regretting Xavier's death. Otherwise they made him very different from his complex character even in the first books.
Cyclops should not have died. Granted, I had never been thrilled with the movie version of him, but in the comix it fell to him to be the leader after the Prof left. What that did to him and his relationships within the Xmen has made for some very interesting plots. The fact that Halle Berry is not the leader of the Xmen absolutely sucks. Besides, Storm has never been like she was portrayed in the movies. She should have been strong and not scared of normal humans. (she was worshipped as a goddess and had a mohawk, that's pretty hardcore!)
Grammar did decent with what he had to deal with. The suit looked like, well, a suit the entire time. They should've just gone full on Beast (where he looks more feline). I did like where he became liason to the White House. That was cool.
Iceman's transformation was horrible. What did they do for that effect? Take the plastic toy and pose it? It was horrible.Colossus and Juggernaut should've fought. I was disappointed that they didn't. Since they took so many other liberties with costumes and such in the movies, they should've just dropped his helmet too.
They also botched Wolverine's character. He's not so gaga over Jean that he would simply forget Cyclops for half the movie. He found his shades! He knew he had been there! Scott was their field leader, not someone that can simply be missed for so long. He also wouldn't have cried like a little girl over the prof. Maybe a single tear down the cheek at the funeral, but not weeping more than Storm.
I thought the adaptation of Phoenix was creative, but lacking. The comic book version would've been too much to adapt to movie unless the entire movie was about her. Personally, they should've just left her out of this movie completely, developed the relationship between Logan and Cyclops that had been developing in the first two movies, cut out the sorry rendition of the Danger Room, done some wicked-cool stuff with Iceman (he was one of the original Xmen for Pete's sake), really introduced the sentinels instead of this stupid vaccination, forgotten about Angel (he was kinda pointless anyways), and instead of "spikes from his arms" man, they shouldv'e brought in Omega Red. And fix the Fastball Special. I was throughly disappointed when Colossus twirled Logan up in the air instead of throwing him as in the comix. Do it right or don't do it at all. If they wanted Storm to be a leader too, then they couldv'e very easily had two emergencies (like they do in the comix) and give one team to Cyclops and one to Storm (team A and B). Then you can focus on character development within each group.