Cool concept. The game looks very nice as well. However, I don't really understand how to play it. The enemies only seem to spawn once I've emptied my gun, but then I can't shoot until I've retrieved all bullets. But once I have retrieved all bullets, I automatically lose.
I do like the idea of a game where you have to retrieve every shot you take. It makes you think much more before you pull the trigger.
A quick tip though, make sure to normalize the movement input vector, before you multiply it with the speed. Now, when you walk diagonally (holding both w and d, for example) you move faster than while holding only one button. The magnitude of the movement vector (before you multiply it with the speed) always needs to be one, to ensure the output movement vector actually has a magnitude equal to the speed.
I would really appreciate it if you would have a look at my game as well :D