After having thoroughly explored all of the new zones in legion, I can confidently say that they suck. They all suffer from the typical Blizzard "polish" that plagues games like Overwatch. On the outside they look great, but after going in and picking them apart you realize how much depth they lack. These new zones are not memorable in any way, shape, or form, and at times are a chore to run around in.
I could probably write a 20 page paper complete with diagrams, etc. on why they suck, but I'll just leave it brief; compare a zone like Highmountain to Howling Fjord. Howling Fjord has such a unique identity and personality that Highmountain can't even begin to compare with. The lift going up from the Horde starting area to the main zone, the Alliance boat ride through the archway, the giant Vrykul castle and town outskirts in the middle, the lift going down to the walrus people area, the northern zone with snowy hills, etc. Highmountain has NOTHING unique or interesting, save for maybe the Tauren "city" you can walk around in.
Anyways my point is that when someone says Howling Fjord you instantly think of all the above things mentioned. When someone says Highmountain I don't honestly know what to think of. It lacks huge amounts of depth that is obscured by pretty graphics and a level of "polish" that many will fall for. All of the zones fall to this.