I think the game is very uinque in style and gameplay, that's very good. I think the enemy AI has potential. Just let them do damage and/or give the player a reward (score would be a most common solution) for killing them, then this behavior will make it very fun to hunt them down. Also, the game has a cool style!
I strongly recommend going for more common controls, though. I played with keyboard and yeah... Z is on the German keyboard layout in the upper row, not on the left bottom (I just noticed this has been mentioned above. I leave it here yet ). And all that confusion with S, X, and A... typical controls are E/F for enter vehicle, W,A,S,D or arrow keys and space/Ctrl/Alt for firing/jumping. Even when you can re-bind the keys as a player, I personally think it's important players can start withi intuitive controls right away.
It's just a suggestion, of course, it's up to you