This toy has lots of promise. We did lose one ball already, but we've added the Grimm's Black and White set, the Grapat Color Ball (and Bowl) set, and a Jingle Ball from a Plan Toys rattle. We get as many balls going as we can. Some skip the order because of their diameter allowing them to drop sooner. Sometimes a few get backed up and it looks like a colorful caterpillar in the tracks. My baby even tries to turn it upside down and roll them up the slope of the track. We'll be looking for other things to roll down the tracks. I don't love that there are five balls and four resting slots, maybe we are expected to lose a ball.