Young Thor, an impressive game that's one of the best values $5 can get you on the PlayStation Network.
A side-scrolling brawler, Young Thor is instantly accessible, but with enough depth to avoid making the experience too repetitive. While it's tempting to simply mash the Square button, developer Frima has done a good job of scaling the experience, introducing new enemies that demand new strategies. My own play style evolved as I learned to add more jumps and dodges while chaining Thor's lightning magic into combat.
There's also a rudimentary XP system that boosts Thor's basic stats. However, don't expect to use your XP in any novel way. You can't customize your character, nor do you learn any new moves. The leveling seems to exist for the sole purpose of encouraging replays. Somebody out there will want to achieve a level 100 character, right?