This was a very neat game! The gravity switching layered on top of the perspective shifts made for some really interesting puzzles. Cubey controls well, and the visuals, while simple, work great for the concept.
My biggest critique is that its too easy to soft lock on puzzles involving the boxes if they accidentally get pushed into a corner. Maybe adding a way to pull the boxes would help with this? Additionally, platforming in the perspective shift could also be finnicky, especially when the platforms were small. Putting a shadow underneath the player would go a long way in helping it feel more intuitive.
All in all though, these critiques are mostly nitpicks. I was able to make it to the end of the game and had fun puzzling out the later levels. Great work!