Also, some way to make the response to the down key quite so...quick. I have ruined so many good games by holding down the down key for a fraction of a second too long. Maybe make a timeout on the downkey for a second or two after using it?
Different sized boards would be nice, and badges. Maybe keep the pieces secret until you get to them so there is some kind of surprise. There could be a versus mode against the PC like in Doctor Robotniks Mean Bean Machines (if you've ever played it, if not then check youtube). Apart from that I have no idea.
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