Marvel Kapow is an interesting approach to the licensed game idea. Most superhero games aim to directly control the superhero, letting the player experience being them, but Marvel Kapow is a much more casual, abstract experience, instead simply using the Marvel license and its various heroes to set up a few different minigames across a series of levels. The games vary from Captain America's Brickbreaking shield to Iron Man's repulsor ray blaster and Wolverine's claw slash, but the basic idea is that you're defeating incoming enemies while switching from hero to hero on the bottom of the screen.
Scoring has a cool combo feature that enables you to build up a higher score by defeating enemies all in a row, but unfortunately, that's about all the complexity here -- just play the game and try to score as high as you can. The games overall are a little boring, and the only way the title ramps up at all is just to throw multiple games your way at the same time, and then rinse and repeat for what's probably a little too long.
Still, it's a fun distraction, and the game's currently on sale, just US 99 cents for the iPhone version and $2.99 for the iPad. I'd recommend you try the free version first, however -- even if you're a huge Marvel fan, this gameplay might be a little too abstract (and to be honest, dull) to even capture your imagination.