you should add a buy 5 button to zombies. It gets annoying having to press the +1 button all the time. also there should to be further upgrading of company upgrades. The game really slows down once you have bought them all. well after a while. Finally, champion zombies might be a nice touch too. However in that idea there needs to be a limit on champions you can use in a battle. I think these ideas will make the game a LOT more fun!
 "Corporation Inc."){kind=icon}
 "Zombies, Inc."){kind=icon}
 "Tap Heroes"){kind=icon}