Great visual style and sound design! The gameplay is really fun. My only minor issue was that the upgrade and weapon-switching system felt a bit confusing at first.
Seeing the ammo count for all weapons right from the start, even when only one is available, is a bit misleading before you figure out how things work. It might be better to either hide the ammo for locked weapons or allow the player to switch to them and show a message that they need to be unlocked in the upgrades menu first.