Not much to say that hasn't been said already by many others. But I'll throw a few words anyway!
Fun experience, cool design, few hiccup oopsies like the physics_process thing and the upper edge etc. Quick and easy fixes. As a rock and metal guy I appreciate the choice of rock for the game lol.
The only things I'd personally want to see was more info (stats, tier?) on the guns, and not having to spam space for best performance. My thumb muscles hurt now haha.
I can imagine this game being a bit arcade like, where the player plays through a series of rooms (through different acts?), bringing a lot of variation in enemies, scenery and a new boss for each act.