Rules are simple, but the game is challenging. It's well-programmed, so it behaved consistently, the only hard thing is the puzzles themselves, as it should be. Loved it. I can imagine a few expansions to the tool set for more puzzles, like prisms, so I hope there's a sequel.
(Perhaps one slight nitpick is that the mirrors rotate when you click on them... and also often when you click them to pick them up. It's not enough of a hassle to cause problems, just annoying. Perhaps some other way to rotate them, and perhaps allowing rotation in both directions, would be nice?)