This was fun! Three bosses that each had their own unique feel to them, thematically, artistically, and in terms of gameplay. That variety was nice, and the last one especially was a fun challenge. The menu is also pretty nice.
I'm going to repeat what others have said: the controls would definitely benefit from a quicker response time. Also, when holding down the fire button, the sound doesn't line up with the attacks; a minor bug, but it's in your face pretty much the whole game.