Zombie Driver, a GTA 1 style game where you drive through streets through hordes of zombies. Too bad the only missions in the game are "drive to this spot and clear out the zombies to save a few people". Also, the game is just too short - 17 missions, all being more or less the same, all just taking a few minuts. Getting all the 12 achievements took me 3,3 hours, and that's with two playthroughs where I did all sidemissions (which are either "clear this area too" or "save the people within x minuts".).