Nice job on the game. If you die, you don't seem to loose your coins. You just can't access them in the menu but if you start again, you don't have 0 coins.
Minor bug I found: one enemy glitched through a wall into my room.
I think what this game needs is speed. Crank everything up, player speed, enemy speed, etc. I felt like I don't really have to fight any enemies as I can just walk past them. Everything is so slow, it makes it less fun. Try playing around with the speed settings on your player, enemies, weapons, etc. It started making more fun once I got upgrades but enemies where still really slow. :)