Very nice graphics and animations. I like the use of positional audio too - audio effects like that get overlooked in too many games.
For the keyboard controls, I would have liked to have had a WASD option. The button mapping on an X-Input gamepad is really weird - movement on the left stick is fine, but shoot is assigned to d-pad up and the face buttons are all some weird sideways inverted movement.
The boss needs some sort of visual indication that it's taking damage and eating a death from that initial popup from the bottom of the screen with no warning felt kind of cheap. Other than those issues, the boss was fun and the artwork is great.