Hey, Zhuckly! Thank you so much for your very detailed feedback! Definitely, there is a lot work to be done yet!
The bosses will be redesigned at some point. The anticipation animation also needs some work. In fact, everything already there still needs a revamp and rework. The upgrade system is very basic, just to keep things functional. Actually, I don't think a boss can instant kill you unless you have just one hitpoint. But that is desired to be this way. An hp system based on bar leaves to the player guess-work about how much damage will be dealt, which can surprise. However, with the current system, you know exactly how many hits you are to take (number of colorful hearts), before dying. This decision was taken at the early beginning and for now, I have no plans to change it. But we will see!
Indeed! You do start with only two hitpoints, but you can increase it and refill it, depending on the powerups you have opt to.
Again, thank you a lot! It's a good reminder and motivation to improve the game.