Pretty fun.
When I first saw this I thought it would be exactly like many other similar games with starting off with a gravity switching mechanic and then adding to the powers as the game progressed but I was surprised to find that all the puzzles have to be solved with that one skill alone. I like when games like these make you have to rethink how you can use your power.
My only complaint is that, for me at least, the difficulty curve fluctuates too much. Some levels are too simple then followed by a challenging one but then there's another simple level.