This is the kind of game I could sink a lot of time into. I like the concept a lot, and your implementation is solid. One issue I had was that when I selected a tile, it was immediately mirrored on the X axis, so tiles that I thought would fit actually wouldn't, even when I rotated them all around. Other than that bug (which will be easy to fix, I'm sure!), I enjoyed the game. A little bit of background music would go nicely with the slow, contemplative gameplay. Nice job!