I enjoyed this game a lot!
Solid gameplay loop with great snappy controls!
For me the art steals the show, what a nice looking game you've managed to make!
I wasn't quite sure what the upgrades did exactly, but that didn't stop me from really enjoying the game.
The first few times you killed an enemy and got hit, the game would freeze for a couple of seconds. I'm guessing it has to do with needing to load in all the particle effects. Might only be an issue with the browser version though.
One of the better games I tried! Great work!