As I've played more of the game, it is a lot of fun, but there are a number of similar abilities amongst the characters that make them seem like clones and also takes away some of the fun when playing with others. You don't need Hulk and Thing on a team together unless you're doing training missions. Worse, melee characters will be fighting to see who gets to attack the grunt first.
Then there are some abilities which hinder other characters. Jean Grey has a telekinetic pull. This is a great ability, but not if you are playing a melee class like Wolverine or Iron Fist, because her pull happens faster than their attack.
Likewise, the game is a bit glitchy. Certain powers won't lock on to an enemy, even if they are right in front of the character, instead hitting one off screen. Worse, there are charge moves, where the character rushes forward to attack an enemy. If another player or a piece of debris is in the way, the attack won't connect.
Also forgot to mention: some of the alternative costumes are great (Iron Fist is Ancient Chinese, Hulk is Red Hulk), but others REALLY suck ass, especially given the options.
Deadpool's alternate is him without a mask. Really? You couldn't have just given him the Marvel Girl costume, or the Black and Orange X-Men style costume?
Penance? Its Bobby with only pants, as seen when he was in prison. No Speedball for you.
Storm? No Mohawk, no awesome silver costume from the cartoon. No, its a white version of her current costume, but showing midriff.
The worst? Wolverine. With the hundreds of possible costumes to choose from (Patch, Weapon X, Samurai, Old-School Orange, Old Man Logan, AoA, etc.) they give you the black and yellow Ultimates costume.