Amiens was an important town in the Middle Ages, but nowadays is rather inconspicuous. It has a lot of modern buildings (and a second WHS, the Belfry). The 13th-century Cathedral is located in a built-up area, among shopping streets. It's in good condition. The facade is its most striking point: with many fine sculptural details, especially above the doors.
The inside of the church is like a religious art museum. There's for example a fascinating sculpture of a weeping angel (which became a popular postcard for soldiers in WWI). Also remarkable is the alleged head of John the Baptist. This relic was brought from Constantinople by Wallon de Sarton as he was returning from the Fourth Crusade.
After visiting this site, I wondered how many Gothic cathedrals the List can handle. And which one is the oldest / purest / biggest / most beautiful? In his Comparative Study Of Gothic Churches, carried out for ICOMOS in 1988, the distinguished Swiss expert Professor Peter Kurmann identified no less than 15 churches eligible for a priority list (and that doesn't include the ones inscribed pre-1988, like Amiens and Chartres). So there are still more of those to come.
From his report, we also learn that the cathedrals of Seville, Milan and Cologne are the largest Gothic cathedrals in the world. I would say that Amiens' unique selling point lies in its sculptures.