Good game, but super glitchy. 2/5. Guns constantly stop shooting, some zombies won't die after many, many clips of shots. The aiming system is okay. Your bullets should come from the house, not the sky. Since they'd be coming from the house, the should continue. Like if you missed, the bullet should keep going and be able to hit another zombie.
Here are two suggestions. Add a "speed up toggle." Engineers have to wait forever for the handies to get to their tower. Secondly, let us advance more than 1 wave early at a time.