This was probably the game I spent the most time with! I agree with every point Verburner made, although for me upgrades randomly got bugged, so the first few damage upgrades all gave me 5 and then at some point I was at 1200 :P
It also happened to other stats as well, like bullet size and shot delay.
However, despite that I'm really impressed with what you made in one week, hats off man :)