You gotta love these kind of games!. But there is room for a few improvements.
1: The gun is pretty much useless, because it only has enough ammo to shoot the early zombies
2: For the earlier cars the fuel upgrades hardly does any difference.
Not really my kinda game, but this is a pretty cool twist on this genre. The only thing I don't like is, that the AI is making moves that's not on the map.