At first I mostly thought the level design was a bit bland. The controls work fine, and the art and music are incredible, but there were quite a few little niggles. Not being able to restart levels annoyed me, since the rating + timer seemed to ask for it. Also, the opening of Level 3 was very cruel.
But with the secret path, most of that was blown away. I really enjoyed the esthetics of the secret levels and the story they told. The rotation mechanics were implemented quite awkwardly and seemed unnecessary, as I had no trouble traversing the levels while avoiding them., but that felt minor. But then the "leap of faith" level, was an unsatisfying ending. I have scoured the second to last level, feeling that there had to be more. But I could not find it.
Still amazing work, regardless of the somewhat unsatisfying ending.