pixeljunk: Shooter
Fantastic PSN game by the makers of Eden. Shooter is set in an underworld set of caves where you are sent to rescue your team. The major twist that sets it apart from other similar 2d arcade shooter is that there is a nice "physic/liquid" technology in the game.
Let me explain: since you're underground, there is lava And there is also puddles of water. If you shoot a hole and get water on lava, it will cool it down. See more in the following video.
What I found is the game is challenging enough at 1st to keep it fun but it gets more and more challenging as the levels progress with the introductions of better enemies(magnetic dudes, lava shooter, Super bosses).
So if you have a playstation 3, then please try it out!! 9.99$ is a steal!
I rate this game: 9.5/10 not perfect because I would have liked a melee combat for multi-player. but co-op is really what Pixeljunk aims for.