I like the concept of a shoot'em up arena with exploit-like upgrades. In fact my own game shares some similarity in design ideals. My major concerns about the game are more about gameplay. Enemies can spawn on top of the player and I was caught off guard by it. I also ran into a bug (or was it intentional) that slowly killed me while no enemies were left on the screen. I think I would try again if these issues are solved. Good work.