In the past we've covered a number of excellent top down survival shooters. Most of the great apps in the genre, like Final Fury, Gun Bros, and Bullet Time HD, are graphically intensive games geared towards hardcore play.
Monster Shooter's cartoony approach makes for a refreshing take on the genre. All of the usual survival shooter conventions apply to this app. There are tons of guns, more enemies than guns, and more levels than enemies and guns combined.