Very impressive prototype. I overall like the game but suck at giving good compliments so I'm just gonna air out my grievances.
Combat and movement feels a little too complicated but this is likely a skill issue as I found myself slowly getting better the more I played, but maybe a "slower" tutorial level would be good?
Upgrades were confusing to me as well because I wasn't sure if they applied or not, I also found it weird that selecting an upgrade under "MOVES" removes the upgrade under "MINIGUN"
I had an issue with the game resolution on linux on a multi-monitor setup, the resolution would be set to the combined resolution of both monitors and looks super zoomed in, Turning off fullscreen makes it work on both monitors, fullscreening on the second (small resolution) monitor causes the zoomed in effect, but fullscreening on the main monitor works fine.
I'm using X11 with DWM as my window manager if that makes a difference. Single monitor is fine.
All in all really enjoyed playing and beating ass.