Ok, I just remembered why I thought your game was too difficult, ant to be honest this is because of my personal preference. I'd rather have the health filled up at the start of a new fight. I know there is a powerup that does that :)
Other than that, the game is fun, controls responsive, upgrade mechanic engaging. It did pretty good on BRJ, and replaying it now I am reminded why. Also- kudos for the web build. My BRJ game was the first one I did a web build for, and now I'm gonna try to do one for all of my jam games.
Btw (shameless self promotion here) feel free to check out my submission. It's an earlier game of mine, but something absolutely different from my BRJ thing.