I think the game is truly brilliant, I love all of the games in series! Especially the first one, as it was easier ;) Personally I think the boss is almost impossible. He must have 10 hp, then second phase (if there is such thing), and 10 more. Checkpoint between the two.
Oh, and also, I think the third game must be more of exploration game. I want to see open-world with polly the frog :)