I'm afraid you stretched much more than the surface, my friend! We know that there's some lack of balance in the guns in the game and even the number of enemies needs a tweak. We will release a patch with some fixes in the next days, hopefully it will sort those things out!
This game was made as a college project, so we were not working exclusively on the game. Although it is "released", we know there's a lot of things that can potentially be fixed.
Thank you very much for playing!