Really nice and polished game in my opinion. Although i swear i was a bit confused when i reached what looked like the edge of the map because i thought this was infinite or something like that. Also it would be better to have some decorations or different rooms maybe to make it more interesting. For the wave 4/boss/whatever thingy, the switch thing that teleports you to the other room can maybe be a bit clearer.
Other than that stuff though, great fun game, really nice artstyle, really nice music and sound effects, good controls, nice that you can shoot to open the shop menu and stuff, and the enemies are also cool too. Keep up!