Good Special Effects.
The effects were cheesy and downright fake looking in most of the film. It's pretty bad when Wolverine's claws don't even match up with his hands in the bathroom scene.
Aside from the special effects, I did enjoy that characters. I liked seeing the mutants that were never introducted in the X-Men Series. Gambit, Deadpool and The Blob are just a few that are featured in the film. Also, we see some of the younger mutants like Cyclops before they reach their full potential. The film does follow most of the comic book, which will make most fans happy.
Overall, it's still a fun film and the characters make the movie. Just hold your breath when you see a cheesy special effect.