Personally I really liked it, although I know it's been panned by most comic geeks, or atleast the vocal ones with an internet connection.... I've heard that there was quite a bit cut out, which means the DVD release will be a far better movie in the long run. Quite a bit of characters got killed this time around, which is fine since it's (theoretically) the last one in the franchise, not counting spin-offs. And unlike the comics, I'm not too worried about Jean coming back to life 37 more times.
The main complaint I initally heard was that too many liberties were taken with the characters, such as Juggernaut becoming a mutant and the Phoenix being part of Jean's psyche. But really, does the general movie going populace need to deal with Xavier's magic crystal-powered step brother, or a mystical space bird/clone. Some things really only work in the comics and should be kept there.
Of course, now I hear people complaining because the story was all pieced together from the comics and there wasn't anything original in it, so I guess you really can't please some people.
So yeah, the fight scenes were cool, there were some corny lines but that was to be expected, there wasn't really enough story, but I'm eagerly awaiting the director's cut/special edition. X-2 was a better movie, but this did a good job of wrapping up the series, instead of just being another sequel to prolong the franchise. Closure is good.
Really looking forward to Superman Returns, though. Every ad and preview I see makes it look better and better.