I did tell you about stuff you could change, but maybe not directly enough:
- add a checkpoint between levels for people like me who want to see the ending but don't want to repeat levels they already completed when they die
- try to find a way to better communicate when you hit the boss. Against regular enemies it is fine because they die in one hit, but against the boss the player needs to see that what they are doing is affecting the boss (there are common ways to do that, like making it blink white, adding particles, or simply displaying a life bar)
I'm sorry if my comment upset you, I just wanted to share my experience with your game that, I insist, I enjoyed (and rated well).