Samarkand is one of those cities which could easily be in the list a couple of times had they wanted to. And in a way it might have fit the place better, as Samarkand is better understood as a set of masterpieces that happen to be in a city. That is especially true compared to the likes of Bukhara or itchan Kala which shine because of their cohesion.

I would say there are 5 main components in Samarkand which could've had a decent shot to get into the list. 

1. Gur e amir, this is the accidental  mausoleum of the timurid dynasty (it wasn't built with that intent). Its rather small size is easily forgone once you see the luxurious decoration of the interior. I found it gave the best glimpse into the luxury Timur's palaces must've sported, which is otherwise hard to spot in Samarkand. Check out the jade wall tiles!

2. The Registan. The most iconic monument in Samarkand is indeed impressive. Here we get to see the famous timurid like for the monumental. Compared to later styles in the region the use of brick gives the madrasas an almost mellow colour and a much more elegant though less colorful appeal. It's perhaps the poster child of timurid architecture. I cannot talk about the interior because I was unfortunately not let in.

3. Bibi khanym mosque. This mosque was one of Timur's jewels for Samarkand. Built with the spoils of the sack of Delhi, the mosque was absolutely disproportionate. Unfortunately the fast and gigantic construction proved too fragile and started to fall down almost inmediatly. By the 20th century there was very little (relatively) of it. It has been restored heavily since and I calculate that roughly 50% of the old mosque can be seen nowadays.

4. Shah i Zinda (photo). This is imo the actual most important site in Samarkand and it has miraculously survived the ages pretty well. Shah i Zinda is a procession of mausoleums which eventually lead to the tomb of quth ibn Abbas. It's an open air gallery with a like for splendor. A chocolate box of glazed ceramic domes.

5 afrasiyab. By far the least impressive site in Samarkand is perhaps one of the most important. Afrasiyab Is the archaelogical site of the old Samarkand which was razed to the ground by genghis khan. Taking into account that Samarkand was at certain points in its early history one of the major cities of the world, this archaelogical site is of worldwide importance. Nowadays the most interesting artifacts can be seen in its rather small but interesting museum. The most interesting artifact are the vibrant frescoes.

Now, the bad side of having all this places under the same umbrella is that it leaves very little margin for corrective behavior, which is honestly very necessary in uzbekistan. You see the Uzbek government doesn't restore buildings rather it rebuilds them. Destroying in the process what was previously there. It happened in Samarkand in the shah i zinda complex, to the abject horror of the international community, and I firsthand saw it happening in Bukhara.

Were shah i zinda it's own site, Unesco would've probably expelled it already as retribution for the horrific restoration. However Samarkand has so much going for it the government could destroy 50% of it and it would still be worthy of inscription.