You did a great job with making basic shapes look very pretty with good lighting and colors. The grain also adds a lot and the UI is well-designed (I also like the little cursor-responsive effect in the menu, that's a nice touch). I think the player character could use some squash-and-stretch when moving and falling for some extra juice though.
While the level design & character controller are well done, I didn't enjoy the main mechanic; it made the game hard in a frustrating and somewhat dizzying way and I think I would like the game more if it just had the level element switching based on the direction and no screen flipping, with some tighter platforming in exchange. The spacebar-for-flipping suggestion below also sounds good to me. I'm not a big platformer player though so it might be just me :)
I also wish the restarting after death was a bit quicker. Nice job overall though, it's very stylish and the gameplay has good potential.