Really great idea for an approach to player health and the theme as well! Really challenging but easy to get into, and the gameplay is nice and snappy. I especially like the rouge-like elements such as the upgrade-downgrade system at the end of each wave. Music is great too!
If I had to point out something it would be minor issues with bullets. Sometimes enemies would shoot them when the player was right next to them, leaving very little time to react. this could maybe be fixed through a quick tell before an enemy shoots.
That's a very minor problem though, the game is a really fun arcade shooter and has a great take and variation on the theme! nice work, maybe one of the best from the jam, but I've yet to play other games!