I wouldn't have recommended buying this game as a new release, but now the price has dropped, it's definitely worth playing.
It's a mostly short-range action game – even the “energy projection” power set is barely useful outside of melee range, and there aren't really any areas open enough for ranged attacks to be significantly useful. The combat can sometimes feel a bit sluggish, particularly in your first playthrough, and the lack of canceling on a lot of basic moves can sometimes feel like input delays when you feel like you should be able to interrupt or cancel into another action.
Inexperienced gamers, or those not familiar with fast-paced action games, may not notice this, and the experienced action gamers can adapt if they're willing to give it a chance. As you get more experience with how the game works, it starts to feel a little less choppy.
The only complaints I have which remained after I'd played halfway through the game are some frustrating framerate drops during intense moments, and the fact that some of the supposedly high-level powers you unlock later in the game end up being decidedly lacklustre when used against one of the bosses during the (surprisingly awesome) endgame sequence. If you chose wrong at one point about halfway through the game, you might find it almost impossible to actually beat the game – EVEN if you're playing on easy (and yes, I turned the difficulty down to test it).
It's also quite a short game, but with three power sets and three characters which can be selected interchangably, and with several options for how to develop your character with each choice of power, there's a good amount of replay value even without considering the unlockable items you can collect, the two possible endings, and the new game plus (NG+) mode.
NG+ is, if you're not familiar with the term, an option that allows you to replay the game using a completed save file, unlocking more content and starting with a fully-upgraded character. It lets you perform insane combos and totally dominate the earlier enemies, and also helps to ease the transition to higher difficulty levels, since the game allows you to turn the difficulty up on NG+ and bring all your extra gear with you.
Some of the collectibles also make a difference, since most of them are modifiers to your character's powers. Most of these are “X-Genes”, which have a direct influence on your characters abilities. They might interact with your powers, adding a damage bonus and special effects to your attacks, or they may give you things like health regeneration, or increased damage resistance as you fill your power bar. The X-Genes are all tied to existing characters in the X-Men universe, and you're free to mix-and-match to build your ultimate mutant powerset. You can also get costumes that are “inspired by” the outfits of the various characters, and if you combine a character's X-Genes with their costume, you get an additional bonus where you can enter “x-mode” which is a character-themed additional improvement to your character. It chews through your power bar pretty fast, and doesn't generally offer enough benefit to offset the cost, but it's a fun bonus to use if you want to feel more like your favourite character. There are also collectible character bios, which are fun for the fans and helpful to people who don't know everything about the X-Men universe already.
The flaws in the game are bad enough to hold it back from being truly brilliant, but they don't destroy it, and if you're willing to give it a chance, it can still be fun.