Very dissappointing; unless you're a huge X-Men fan skip this fairly awful game.
The combat is mediocre. Lots of button mashing. The special mutant powers are mediocre. They don't look great and they aren't extremely useful.
The RPG element (character building) is a bit odd, and doesn't really make a whole lot of sense. You build you characters special abilities by dumping experience into them, and you develop new abilities in a "tree" system, which isn't innovative, but sort of interesting.
The "gene splicing" is just plain stupid. You can load four different "genes": offensive, defensive, "energy" (or other, whatever you want to call it), and finally, costume (which is in no way a gene), and these can be leveled up as well. The goal here is to load all four genes from on single character to gain an additional "power". This "power" is generally a boost, and it's pretty lame. This could have been much more exciting. On top of this, if they wanted you to build X-Men powers, why not just play as X-Men and level them up? Most of the characters powers are pretty similar including, gaining offensive strength, burn damage, ice damage, increased defense etc. They help in the game, but aren't flashy and not diverse enough to be interesting.
Graphics - The graphics on this game are pretty poor for a PS3 game. The backgrounds are mediocre lacking diversity and a significant amount of detail. Some of the character designs are awful, for example, Cyclops' mouth stretches from ear to ear and his lips are way out of proportion to the rest of his face.
Sound - The sound is good in battles, but poor in dialogue. This is in part due to the poor voice acting. Some of the dialogue is grossly over acted. Some of the accents are horrible... Gambit's accent is awful; he doesn't sound Cajun at all. For some inexplicable reason Emma Frost is British
Continuity - As noted in other sections the continuity with the X-Men Universe is not particularly good. The voices are off and some of the characters just don't look right... Magneto in particular has a very odd costume. It's really pretty simple to just lift the current costume designs from comic books
The villains at the beginning are the MRD and U-Men, which haven't been major villains for the X-Men in the past couple years (but that can slide because there are still many stages I have not completed and there may be additional enemies).
Recommendations for Devs - Go back to the X-Men Legends formula. The games were simply better and they seemed to follow comic book arcs, which makes the stories a little more enjoyable.
Diversity of characters is only good if there is diversity in abilities and power sets. Marvel Ultimate Alliance made this mistake and just copied characters abilities over and over, but put them in different costumes. Destiny does this to a lesser degree, but it's still not good
If you're an X-Men fan and you want to play this rent it for a weekend and get your fix. If you're not an X-Men fan pick up Spider-Man: Edge of Time or Batman Arkham City.