We have similar games, maybe we can compare notes. I got to 13,000 before it lagged out my game. What is the point of corpse lifetime? I think that might have hurt my framerate the most.
It also might be really cool to be able to upgrade the enemies' stats manually. It felt fairly well balanced in the beginning, just ramped up a little fast once I unlocked double shot. Are enemy upgrades dependent on player upgrades?
Nice game. It would benefit from just a little bit of music or sfx, and some better looking UI. Also, adding bloom to a WorldEnvironmentNode is an easy way to make simple vector art look a lot better.