Well, this is a really cool, polished game. I think I had an issue with the timing on the reload mechanic. It just didn't always feel like it mattered and just jammed at random... So that's a thing maybe? I could just suck. Other than that, it's very hard. I don't know if there's more than one level but if not, I did not see more than the one passed the tutorial, it's hard =D
Great work though!