Comic fan service, great RPG-infused brawler, and an overall good time. A little too short unless you like repetition.
Marvel is a powerhouse, especially nowadays with many more blockbuster hits in the theaters and subsequent licensed video games. Unfortunately none of these games were any good. Spider-Man 3 was so-so, Iron Man was putrid, and all others recently released aren't even worth mentioning.
Additionally, the beat-em-up "brawler" (or hack-n-slash) genre has not seen a decent game, probably, since this one. Viking was pathetic, Conan was bad, and I'm sure I can name a bunch of others (including Spider-Man 3) that didn't offer anything useful. Mostly because there's no CUSTOMIZATION. In order to prevent repetition, you need to switch it up, have the enemies get tougher, and also allow your characters to rank up and get new powers. Luckily, this game has all that, so if you're into these types of games, you need to check out M:UA.
With a vast list of characters at your disposal, its great to finally get the opportunity to play as all of your favorite characters at once. I love Spider-Man but I'm also an avid Hulk fan, so only in this game can I have both and randomly switch between them. Please note: I downloaded the "Hero Pack" on XBL, which you need to do if you're a comic fan (800 pts, adds many popular heroes and villains as playable characters, and 250 extra achievement points). You get 4 slots to build your own "team" and if you make a classic team (or known team), they get benefits from each other (make an x-men team or the Fantastic Four to see what I mean). Each "slot" (not necessarily a specific character) levels up, a la RPG, up to level 50. You also collect "coins", which allow you to soup up a specific character with specific powers and each character earns new costumes for specific tasks, kills, etc. All in all it's a decently customizable RPG-based beat-em-up.
The level design is pretty solid. The levels are short enough, have enough enemies, and are diverse enough that you don't feel you're doing the same thing twice. Comic fans will love the large number of characters, enemies, scenery (or settings), and even a trivia portion! There are also pretty difficult "comic" challenges, which reenact certain plotlines from classic comics. All in all, you've got a solid 15-20 hours to boost your characters, and easily 40 hours for all the achievements (if you so desire). The biggest problem is that you need to do a decent amount of grinding (RPG term for senseless killing of many enemies for XP and bonuses) to pass all the comic challenges and unlock all the costumes. As a result, the game can get pretty repetitive. I still found it enjoyable and highly recommend it to all brawler and comic fans. This is so low priced right now and worth it, I'd even recommend skipping the rental. Demo it in the used game store (or online if still available) and pick it up if you're impressed, you won't be upset that you did.