Fun game, lots of juice and replayability.
The coin collection sound could stand to be louder, I feel like that's your next and easiest source of juice. The gun muzzle flash also seems a little too big and a little low (it doesn't track the movement of the gun as it goes up due to recoil). And adding some color variation to text/buttons on mouse over and on click will also make the menus (which already look nice) feel better.