Right off the bat, the first thing I noticed was that the camera slowly moves to the right, even when I'm not touching the mouse.
Having to manually cock the gun is a neat idea. Reminds me a bit of an FPS game I used to play called Receiver, which had very realistic gun mechanics.
Very nice SFX.
It looks like enemies sometimes won't disappear, even if they get hit? This seemed to happen more often if I shot them while moving.

I think this is a really neat idea. Good luck.