Nice game overall. It could use a sense of progression (x/x enemies) or level design that requires getting to the end of the stage instead of defeat all enemies. I thought that they would infinitely spawn my first attempt. Typical arena style games might be on one screen so it is more obvious what is going on. I'm not saying scrolling is wrong, just trying to figure out what led to that aimless initial feeling. The enemies can get stuck in on the rocks in the first area (not bad in itself, but contributed to that seemingly infinite feel). I read the itch page again and saw that there was a boss.
The shop exit wasn't obvious to me or maybe I'm just oblivious.
I played up to the tank stage and died a few times there until I gave up (running out of ammo and circle kiting the horde while trying to punch them a few times).
Everyone already mentioned having more feedback, and I agree. When you are hit, the sound is very low and blends into the bg music, and could use a visual effect even a flash, blood, or something. A low health sound could work too if you added a health drop chance. Your attack range also isn't clear.
The enemies also always hit you if they are in range, but adding more ai is a bit of work.
The shop music is great and fitting. The stage music is also well done, but doesn't quite fit the aggression imo. Obviously I can't rate music but the choices do contribute to the experience.