Great game, but it is need to be improved. I think would be better to start after die on a first lvl. I had a bug, when all musics were gone. In your game I can click as fast as I can and I will shooting really fast, but I think would be better to count cooldown of your guns. When I bought new gun, it was maybe was same, or even worse than start one. Also in pixel-art games I use square-shape particles.