Wow. A few frustrating points, but never unfair. I think I would prefer to press a button to start each stage, but your method did give it a sense of continuity.
Overall, fantastic job. Very fun, lots of really different gameplay elements! I do wish there had been a final sequence that used elements from all the different zones, as besides the extra jump most are only in certain areas. But I had tons of fun playing this. Perfect difficulty level, and it stayed fresh throughout.