Brilliant game concept and incredibly fun main mechanic with plenty of potential, as well as a great selection of gimmicks and enemies.
My main issue would have to be the level design. I might've missed it, but it took me a couple of levels to figure out I have more control then just the space key. Moving about and changing your gravity 90 degrees at a time already has a lot of platforming potential without any danger (they're also pretty fun as well to just move around with), so adding a level or two built just to get the player accostumed to the controls could do plenty good to your game. Especially with games like this you want to ease your player into every mechanic, one piece at a time. And I felt that a lot of the mechanics were thrown at me way too quickly and way too early, preventing me from fully appreciating and enjoying them (when they clearly deserve it). As the levels progressed and the difficulty curve has slowed down this has gotten a little better, but I wouldn't be surpirsed if you lose a few players in the early game because of that.
Then again, this game's atmosphere and easthetic is charming enough to keep you playing and feeling cozy. So it's still a pretty good experience.