This game is one of the best I have ever played. I wish the ending were a little more satisfying, but as for the gameplay, I thought it was flawless. My only wish is that I should have had much less time before the guard came back, so that I would have been forced to tighten up the timing a little more! As it was my optimizations turned out to be a little unnecessary.
Edit: I just discovered the challenge version (type "challenge" on the first move). This is exactly what I wanted when I wrote the above! An excellent game, in all regards.