Great!
First, I apologize, my english is not very good yet.
You have created a good game, weapons and abilities are well set... except for car durability, isn't useful really.
I found a bug, sometimes when you put a mine, the zombies are frozen. You can shoot and repair the car. But if you approach at the place where you have put the bomb, the zombies are unfrozen.
Take damage when you go through the zombies makes the game very hard after 20 waves. You need to be caring for your vitality and buy medical kits constantly. Normally, don't like me that.
This makes it more annoying and problematic... but in this game, it's good, really.
Well done (y)
5/5 - Is a funny game.
8/10 - Isn't perfect, but is pretty good.