I like the simplistic approach and the audio is great! However, I will leave some constructive criticism that I hope will improve your game.
- The game felt a little buggy, it didn't run smoothly, mainly when all the balls were at the centre of the hourglass (I'm assuming due to all the collision going on, but not sure).
- I feel like the rotation should be clamped. What I mean by this is to have the hourglass rotate if we actually go around the hourglass with our cursor, if I move my cursor right down the middle (going up and down) the hourglass does an instant flip.
- Gets boring very quickly.