not bad at all! the sounds came together well and the movement was indeed slick. the adaptive music was really cool too.
i do think that it could benefit from a little more tangible feedback. (like when you hit the boss, it should be more obvious that you hit him... like, with a louder sound effect or something, or maybe with a traditional hp bar instead of a number in the corner.) i only say this because for a little while i was unsure if my bullets were doing anything.