I love the overal design of this game. I love the feel of the environment and the concepts of each boss is really cool, even to the tiny details like the quit button being called "Sleep". I also love that intro of the second boss a lot. I think the strongest point of this game is the music, they convey the intensity of the environment and boss fights really well. The art are also amazing as well.
I do have a few criticism though. I think the sound effects are lacking, it doesn't complement the impact of attacks or feel of the environment very well, I also think this game would benefit from a few ambience noises. While I do think the concept of each bosses are very well done, the telegraphing part of each attacks and range of attacks could be adjusted a little bit more, for example, the dancer spinning move could have a much shorter range of attack so that it would be easier to dodge.
Amazing game, keep it up!