First the positives: Neat idea to mix up bosses. The dialogue was witty enough to start off with. Very smooth controls. Nice pixel graphics. Music was okay. Upgrades are always fun. Overall the concept is great - however
(the negatives) I found myself really bored with the game by lvl 34. sometimes brevity can be a good thing. Instead of having so many levels to play - think about only having 40 or 50 and increase the difficulty. I know you made a more difficult mode, but at this point I have no interest in even trying it since even on simple I haven't died once but don't want to spend the time to see 101. Also there is no reason to need so many upgrades. With this concept I'd think maybe 5 upgrades in each category would be sufficient; same thing for the hats.
You have talent, that's for sure! I hope I don't come off as too critical but this particular game lacks replay-ability for me.