I did get the concept, unfortunately, that was inconsistent for me. You've built the atmosphere, but suddenly you change it on the second and third. It would be better if you stuck to an art style and mechanic with different bosses who had their own unique skills.
You also need to improve the way the player moves and attacks (in the first fight). It's pretty uncommon to use the left button to attack in this kind of game. The acceleration was a bit slow compared to the animation speed.
I hope my comment can help you grow. Good luck!