You play as a guy called Barry Steakfries. You travel through time and kill zombies. What more do I need to say? Oh alright I'll say a bit more about it (but honestly how can you not want it after seeing that trailer?).
Basically it plays a bit like Geometry Wars in the way that the key to being good at the game is leading enemies around in the right way so that they don't bite your face off, while at the same time killing enough of the so you don't get overwhelmed. It's all very fun, if a bit simple.
The graphics are very nice and humourous. It all looks like a chibi styled cartoon and it will bring a smile to your face. Something else that will bring a smile to your face is he level themes and Barry Steakfries' lines. Be it his talk about bringing home a zombie caveman to keep as a pet in the jurassic levelor him crying out "eyyyy SMG!" in the Mafia themed level it'll make you giggle.
There really isn't that much else to say about the game as being a PSP mini it is quite small. But at £3.99 you can't really go wrong.