I would really love to hear how this is working out for others, so just give me your opinions please.
For reference here:
First boss: ~19 deaths, which is probably my most so far, with two stars for the level. I died on him more then the level itself.
Second boss-I believe five or six deaths? Not bad at all. An upward dash will evade his bigger tentacle slam and the first two rounds with the smaller ones are easy enough to dodge.
Third boss-not gotten him yet, admittedly. Mostly I was exhausted when I tried, but the nature of his attacks and his arena means it's pretty easy to make a mistake and get yourself killed. I've had no problem getting to the third loop, though, and this patch that'll bring the Halloween level should also bring a few alterations to his moves and an extra shield charm after you hit him the second time. I've gotten close enough times that it shouldn't be a problem after GOG gets that update available. The level's long and has a couple of rough spots, don't have a death tally.
I'll agree the difficulty curve is a bit all over the place, and that is a legit problem with the game. I think it's entirely surmountable if the player has a fair bit of experience with the genre, though.