Myself and a friend bought this for our 5 year old sons for christmas last year.
It looks fantastic and is fairly easy to set up. The kids controlled the cars quickly without them shooting off the track. The biggest problem is the contact, if you dont keep the trigger squeezed the car just stops, it then has to be pushed to get it going again. I have tried changing the wire contact brushes but it made no difference. it seems as if parts of the track have no power. I have pushed each part together without success. As a result my son (and his friends) get fed up with having to get up and push the car every 5 seconds and after about 10 minutes are bored of it. One even saying it was "rubbish!"
As I said its not just my track, my friend has the same problem and the other day my son had a play date and when I picked him up I saw they had the track too - I enquired if it worked ok - it turns out they have exactly the same problem!!!