I would highly suggest you buy this app. It is a very addictive game and a lot of fun. It can get hard fast and it will take a couple of times to get the hang of it. I think the characters could be tweaked a little and you can never have too many guns to collect. The zombies do get the ability to climb over walls, but if you can place your barriers well, you should have no problem dealing with them. Buy this game!
Constrictor5 about Zombie Defense