Awesome game, I'm a little torn on giving feedback because I'm 99% sure there's nothing I can say that you don't already know.
Conceptually it's great. The deck builder bullets and the revolver just tie together really neatly and create a tight game loop that's really satisfying. Balance is all over the shop, you already know that, and I can attest first hand about how badly I dropped the ball on that so no more needs be said.
The art is super stylish, music is a bop and the sfx brings it all together with a cherry on top. UI is decent but lacks some polish as you've also noted already, but really doesn't detract from the experience.
It's honestly really fun, and despite small flaws, there's really nothing glaring. I had a good amount of fun playing this, thanks!