Cool game! I like the concept of a boss rush game. It's not a good decision not to save. If you die it's frustrating to start all over again, It's too hard for new players who dont want to practise. Maybe some playtesting would have helped. I like the graphics. The gameplay could be smoother. If the character gets hit by something the player wants to know what hit him. Because of that the developer has to provide feedback like a flashing player, screen shake, some fire particles if it was a fireball or a punch animation for the boss so that the player knows why he lost. Otherwise the game feels a little bit unfair to the player. With a litttle bit more polish it would have been an extremely good game.
But still a very cool game.
(These are only suggestions to make the game better. I dont think your game is bad. It is not by any means. And I should have provided more feedback for the player i my game too.)