It looks and feels like an old SAS 3 game, but the controls are very awkward. It shoots slightly to the left of the crosshair instead of where you're aiming. Sometimes the shop is simply unavailable, even though you have enough money. Also, make the first wave at least have slow zombies so you can get used to the game. Other than that, it's fine. Fix the aiming and controls, and I'd play it some more.