Well, as you can probably guess from my open, and rather shameless fanboyishness toward this franchise, I loved it.
The characters were spot-on, Beast, Kitty, Multiple Man, Juggernaut, Callisto, hell even Spike (from X-men Evolution) were all nailed and translated more or less perfectly from comic to screen.
Interestingly many of these are on the side of "evil" in the movie, "evil" being the side dedicated to wiping out the cure for mutation. I liked that, since I could see otherwise good mutants lining up to make sure that abomination never sees the light of day.
Also the characters from the previous movies were given a chance to shine, especially iceman and storm and colossus.
The movie also had some great moment for the fans like the fastball special, iceman icing up, a sentinel and the danger room.
I give it an A+ overall.