Amazon calculates a product’s star ratings using a machine learned model instead of a raw data average. The machine learned model takes into account factors including: the age of a review, helpfulness votes by customers and whether the reviews are from verified purchases.
I'd been looking forward to getting this since it was first advertised on Lego.com and it is every bit as good as the advert. Great build, quite complex and very cool. The engine moves and there's 2 gears. I was very impressed with having to build the chain too. Not only that, but it had money off on Amazon!