I'm a big fan of the presentation! Bootup screen was very well done, manual was well-written, all really done well on that front. I laughed when I got RTFM'd too the first playthrough.
--Spoilers Ahead!--
My primary wish is that the steganography mechanic was used in a more engaging fashion. When I discovered that almost all of the rooms had secret platforms, it kinda ruined the "a-ha"! moment I got from doing it the first time, not to mention my fear that I had missed a cookie and would have to do the whole thing again. I feel that more mechanics would have been a huge boon to the game.
I agree with everyone else -- hitbox is too big, and that makes it frustrating to get to the secret level entrances. The controls are very slide-y and feel a bit mismatched to the environment, and I felt more frustrated than accomplished upon finishing the game.