I purchased this toy years ago when my son, who is now 12, was about 3 or 4. For years he collected all of the different marble runs. The two of us would spend hours building cities, and running the marble people down the tubes or knocking the cities over. He played with this game for hours until he was about 7 years old.
I recently purchased two marble runs, one for my niece and one for my nephew and now they spend hours playing with it with their parents. Sure beats that crap you find at certain chain toy stores.