Such a fun take on the theme! Also, the art is beautiful, I especially love the parallax effects.
My strategy that got me through every boss with no issue was to focus on the wheel and keeping up the combo. I basically only looked at the wheel, used every action and dodged the attacks that I saw with the corner of my eye. So, I think that an option to have the wheel in the middle of the screen could be useful, to make the player actually look at the boss, not just the wheel :P