Dead Space 2 is a survival horror shooter. You control the protagonist, a man called Isaac Clarke. You encounter a lot of monsters called Necromorphs, which are human bodies infested with some kind of alien. You can upgrade your weapons and suits at various places, and there are five different difficulty settings you can choose from. The hardest, Hardcore, will keep you occupied for a while. The graphics aren't the most amazing, but they're decent. After the events of the last game, Isaac's slowly losing his sanity due to guilt (if you've played the last game, what he feels guilty about should be fairly obvious). This makes the story much more interesting. The combat in the game is fantastic, and there are a ton of different ways or things with which to attack. This trailer, while not really showing gameplay, is still a pretty compelling work: http://www.youtube.com/watch?v=EtEEa4PU7ok.
Buy it. Have fun.