I like the concept, it's neat to go through the game the first time thinking "this is a bit lackluster" only to see I got a bad ending. Unless you want it to be part of the difficulty, it would be nice to have a way to go back through phases when you target the good ending, as dying will reset the current phase, but harming the boss enough will go to the next one, forcing to reset the whole attempt.
That may only be me but with the various small rotating elements I had trouble locating my mouse cursor on screen at times.