This was really fun, congrats!
I tried playing for a bit, though I never got close to having full upgrades. I loved the rate of progression, and how the "more money at startup" offset the pain of having to start over. I love how a single point in damage already makes me feel considerably more powerful. The progression is really satisfying.
The one problem that is stopping me from actually spending more time with the game is how the bullets become almost impossible to see, as they have the same color as the blue enemies (which also happen to have the hardest patterns to me), and how the enemies bits just linger there forever. It's a nice touch, but it makes new enemies indistinguishable, and the bullets even more so >.>, maybe if the dead enemy bits become a darker color and part of the backgorund it would help, idk, just an idea.
imo, I'd also change the button for the shop for something closer to WASD (and put the music/sfx sliders with the shop. I kept turning the music on and off all the time by accident lol).
At the end though, I'd say these are all minor complaints, you're getting really good at making these, it's fun to see. Keep it up!