My 4 year old saw the race tracks in a pamphlet from one of our other packs, and we decided to try it out. This was the best! It has the marbles and the tracks, and the day it showed up the whole family started building, and now we set time aside every couple of days to see what we can build.
My only issue would be that the pamphlet shows awesome builds, but not quite enough pieces to do them (e.g. We received 14 bridge piece supports, but the coolest build requires 15). Other than that (which only myself and my husband noticed), my 4 year old, my 9 year old, and both us adults are loving this kit and already want more to go even bigger!