I'd suggest getting rid of the purple guys altogether, and centering the board. I think the purple guys not actually doing anything but taking up A HUGE AMOUNT of screen space should be avoided.
It would also be nice to add more skill levels, with the board expanded to provide 6 and maybe up to 10 or so marble(?) positions. That would also necessitate scrolling or perhaps two board displays to see all moves made.
Another thing that would be essential to playing enjoyment (you might already provide this, but it isn't noted here) - a table of high scores for each skill level.
It would also be nice to add more skill levels, with the board expanded to provide 6 and maybe up to 10 or so marble(?) positions. That would also necessitate scrolling or perhaps two board displays to see all moves made.
Another thing that would be essential to playing enjoyment (you might already provide this, but it isn't noted here) - a table of high scores for each skill level.