Wow fun game! Gameplay felt smooth, and the progression felt good - damage bumps were very noticeable as I got upgrades. It was a little confusing at first that hitting enemies was taking away from my health bar, but I was able to get the hang of it before long. The only issue I really ran into was the game slowing down as I got more upgrades - it seemed to freeze for a second or two when I was hitting enemies after I had a handful of upgrades.
Other than that, great experience! You got really expansive with your skill tree so I'm looking forward to seeing how elaborate it gets.