GTA: Bloody Harry
Zombie has taken over the world, but that won't affect you a bit since you are hard boiled and you aren't afraid of anything. You feel that the world is overcrowded and now you want to get rid of the zombies. You are armed with a crowbar at the start of the game, but you would acquire a gun as you press on with the tutorial. Each kill earns you money. You can use the money to buy upgrades or buy better weapon. As you level up, you would have a perk. The game will be tougher, so you would need to buy better guns and if you have more upgrade the weapons too.