You're never hard pressed to find a twin-stick zombie shooter on PSN, but Dead Nation is the one that stands ahead of the pack.
Rather than the gameplay focusing solely on mowing down hordes of undead flesh-eaters in small arenas, Dead Nation actually has a plot, which is supported by gameplay that involves working your way through a level to reach a safehouse, collecting loot along the way, if you can get around the zombies that is.
Weapons are upgradable, giving your guns a much needed boost to power, rate of fire, clip size and such. And when we say "much needed", we mean much needed - the game can get quite tough at points.
Dead Nation can be played with a partner too, which we believe is the best way to play through the game. If you suddenly crave some twin-stick zombie action, Dead Nation's the game we'd recommend.