The upgrade system really ties this together!
The dual (rather triple) purpose mechanic of the currency really ads to your game instead of taking away from it like a lot of entries. The upgrade system means there's a gamble when trying to decide between health and gaining power. It furthermore incentivizes the player focus much more on aiming properly to avoid going low on health, and to have currency left over for upgrades.
The Aesthetic is also simple but nice! I think a good word for it would be 'sterile' but it definitely works for the game and you stick to it consistently. The only thing is that the currency can sometimes be hard to see when there's a lot on the screen, so it might be better to be a little more visible, whether that be making it slight bigger or slightly more contrasting with the background white color.
Bug:
The walls can be "sticky" in a sense that once you touch them you can't move along them, and I got completely stuck and unable to get out a couple times. But I know how much of a bitch collisions can be especially under time constraints.