This game has a really cool concept. I love how you incorporated the theme. I also love that you can buy upgrades, it all comes together really nicely. Well done!
Couple of issues for me though. 1) The gun sensitivity was incredibly low and made it feel pretty clunky to move. And 2) the purple enemies always stayed standing up when killed, so it was kind of confusing whether or not they died, and I keep shooting more than I needed to.
Other than great game. You could really take this in many directions. I hope you continue to work on it :)