a lot of people seemed upset Gambit wasn't in this one. I didn't know the Cajun was such a fan favorite... and Nightcrawler simply wasn't signed on for this movie, which was sad for me because he was my fave X-Men in the comics and they did him well in X-2.
my only gripe with this movie was that since so many new characers were introduced, some of them were not given enough screenplay and development. however, with so many introduced the movie did a good job with what little time they had.
and to whoever said they would have liked to see Havok avenge Scott's death - this would be problematic because Havok was initially against the X-Men and even a part of the Brotherhood before joining the X-Men. I agree with BlueAdonis that the "Multiple Man" James Madrox was a pretty kewl character, and whoever played him did a swell job (he seemed very mischevious and interesting - like when he first was released he followed his eyes on Mystique's ass as she walked past him). what confused me though, was that the Multiple Man was never a bad guy and was in fact a member of the X-Factor...
it was nice to see the director did his homework on the comics - Bolivar Trask, Leech, and Archlight were essentially second-tier characters but pretty big in the movie. what was confusing to me again, however, was that in the comics Trask was not black, Leech was a little green dude, and Archlight was a guy (not some transvestite looking thing). I suppose I am coming off as a bit of a comic book purist but I shouldn't be complaining because they were still nice to see.
the two Brotherhood leaders that joined up at the mutie convention in the beginning were created by the director in the film (the porcupine guy and the fast chick) and he did a good job with them. Juggernaut was pretty kewl, but in the comics he was not English and he was not a mutant.
I was dissapointed how the director took the liberty to kill so many characters. Cyclops disturbed me the most because he was just done so well with the little time he had in this movie, and it was strange to not have him be a major factor in the Phoenix storyline... also I was dissapointed by the screen-time Rogue had, the fights scenes would have been a little more interesting if Rogue and Cyke were in them.
if they were going to do and X-4 I think the next logical villain to introduce in the X-Men mythos would be... APOCALYPSE! that would be awesome, huh?