Interesting Game.
First off, I have encountered a glitch (presumably) multiple times while playing where your bullets count down, but nothing is fired. This has happened relatively quickly into the game both times, so I haven't been able to progress very far.
I noticed another glitch, where pressing escape to pause would not pause the game, and simply blocks the screen.
My other comment is that I think the game's difficulty scaling is a bit fast. I found myself in wave 2, overwhelmed with enemies, without enough upgrades to deal with it.
Otherwise, I really enjoyed the game! I think the soundtrack goes nicely with the game, and makes for a very enjoyable experience.