This game is extremely easy and short. I see what you were trying to create, but it doesn't work especially when it is so obvious of what to do.
There is no reason for the zombie theme; in fact it is a down side to have zombies walk so slowly that the only way you have the attention span to play through this is with the fast forward. I literally had the fast forward on the entire time! Where is the horde of zombies? I came into this game expecting to guide my zombie horde to invade a someone's sanctuary. Instead I had to pick up keys to open a door.
Why did you made a zombie theme? To capitalize on the popularity of it? There is actually no point of making this game. A zombie puzzle game for elementary kids. Have fun.