There should be a survival map, where you don't fail if you die, but you still win. You just earn more exp/money the more zombies you kill and the longer you survive. Kind of like Zombies with Call of Duty. Maybe expand Last Stand? Just a thought, you know...? I think it would be more fun that way.
 "Swarm Simulator"){kind=icon}
 "SAS: Zombie Assault 4"){kind=icon}
 "Idle Tree"){kind=icon}