It's a very solid platformer. I enjoyed it! I like the gravity puzzles and switching mechanic.
The biggest thing I'd want changed though would be some indication of what the opposite world holds. I'm not sure how you might do this (maybe a viewpoint toggle that only affects camera at the start?), but it becomes very difficult to progress through a level when you have to guess what comes next. Of course after a few deaths it's fine, but I'd like to be able to know what's up ahead the first time. The "Thorns" level is the biggest offender of this I think, since a lot of the transitions lead to instant death if the player doesn't move correctly to the newly revealed way forward.
Great job!