Not bad.
I like the idea however the game became tedious for me rather quickly. I think you could use a few sound effects in the game (such as when getting to the diamond) and maybe a few power-ups? Maybe it was just my computer but the piece seemed to move in a jumpy fashion (not very smooth). My only other criticism would be that the whole colour scheme is rather dull and could use a little more life.
Other than that I enjoyed the game and can see you've put much effort into the puzzles which are enjoyable and challenging! I think you should definitely improve a few of these aspects which seem to be keeping the score down a wee bit and release a V2.0!