Thank you so much for this great feedback.
About the floaty jump: I tried to make a jumping mechanic very similar to the old Mario Bros (NES) in which he jumps really high, and the more you press the button, the higher he goes, and as you release it, he falls. Is it too bad? At first I felt like you have to get used to it, it doesn't feel so natural, but I kept it that way despite of this. Do you think it's better to change the jumping mechanics?
About the health system: Indeed it's very hard to play, and if you die (it can happen easily) you return to the begining, what might be a pain in the a** but I felt like it rewardade players who were very persistent, and also added a rouguelike feel to the game. Do you think I should change it? Maybe have a health bar that drops each time you get hit, and when it reaches 0, you lose a heart. Would this be better?
About non responsive jumping: Could you specify a little more? Maybe draw on paint what you mean.
Again, thank you very much.