Really nice game overall, only things I could suggest as improvements are a way to better understand what you're buying in the shop, something like just the weapon type would be helpful, and a way to see the cooldown on firing like a meter during gameplay, since some weapons like the Baboom are a bit unclear on when you can fire again.
The ability to remove some weapons from the weapon pool could be nice as well but with how the multiplier works I feel you probably want the player to sometimes just be stuck with a less preferable weapon.
That said the game is great as is and one of my favorites from this site recently.