Good game. Very fun and simple. Good challenge and well designed puzzles. Graphics and sound contribute well to this game. The only gripes I would have are:
1. Make it so that you can move pieces while on the board. Having to reset to change something might make you lose your train of thought, and you might forget what you wanted to change in the first place, or forget where you placed the rest of your pieces.
2. Make it so that, even if one ball hits the edge of the board, the trial will not stop. Maybe one wants to find out what will happen if such and such pieces are in such and such spots, while leaving another part of the puzzle unsolved. The player can test the one part, and see if what he thinks will happen. After testing he can move on to the unsolved portion of the puzzle.
Changes like these will just overall make a much more convenient and enjoyable playing experience. It will feel like all bases are covered and nothing is missing.