Absolutely great puzzle mechanic, and the puzzles themselves all made really interesting use of it. I think you could really expand it with some other traditional puzzle elements such as pushing boxes or buttons you have to step on part way through, or if you want to get really interesting maybe you could add something that modifies your moves. My only critique is that some of the puzzles definitely felt easier than others despite appearing later on in the game, but that's the criticism I have. As others have said, add some more levels and more mechanics and you could totally have yourself a full blown game here. Great work and best of luck!