Kids vs. Zombies
One cherished cliché of horror movies is that it's only the spunky kids that have a shot at of surviving. Enter Kids vs. Zombies. This really spin on tower defense games is a little finicky to control, but it's a blast. Actually, it's probably more accurate to call this an Alamo defense game.
You're barricaded in, aiming and shooting at anything that comes your way. In this case, three kids hold down the fort--one kid with a nerf machine gun, one with a sling shot, and another lobbing explosives--and you're able to switch between them and control all three at the same time.
Between rounds, you rearm and upgrade your weapons while patching up the walls. More than that, you can boost the smarts of the A.I. so that the other kids you aren't controlling can more effectively watch your back. KvZ is hardly the first game to try this but it is certainly has plenty of flavor and minimal frustration compared to the slightly buggy Attack from The Dead.
Note: This link takes you to the vendor's site. From there, you can follow the link to the iTunes App Store, where you can download the latest version of the software.