It seems silly to pile more praise on a "toy" that has received so much positive feedback; this puzzle/game/toy deserves all of it though.  My son has had this for a couple of years now and it has been a constant source of entertainment.  He pulls it out and it stays out for a week or more before going back on the shelf, and everyone in the family takes a turn at it.  It is a great solitary game, though we have begun to add a timer (a sand filled hour glass works perfectly) just to take it up a notch.