Really enjoyed it. I can see myself playing this for hours if I have a lot of time to sit around. It reminds me of the sort of games I played in the flash era to pass the time. It's really addicting. The music fits and doesn't distract from the game too much (some tracks more than others).
The only major thing I have a problem with is the drop marker -- it's too small and not very attention-grabbing and that makes it more difficult to keep track of it, especially because the player's attention is so often divided between several points in the screen which means most of the time you're not looking at it directly. This makes it unfair and unmanageable to play on the higher difficulties. I think it should be possible to track it with just your peripheral vision.
It seems to me it would make more sense if the game ended immediately as soon as the sand touches the top of the screen.