Lore/Continuity: amazing - e.g. the dwemer great lifts down to Blackreach are in locations where you see just dwemer rubble in Skyrim (TES V).
Scenery/design: also amazing - very beautiful, especially at night with the aurora visible. Muted tones compared to other zones, again very remeniscent of Skyrim.
Harrowstorms: Meh. Visuals are amazing, and the bosses are super-challenging (probably not possible to solo). However, the theme/reason for fighting them is kinda weak, loot is low value (unless you are VERY lucky), and they are a pain to reach for dailies - so far from wayshrines. In addition, once the initial popularity of the zone wears off, it's going to be like dragons in Northern Elsweyr - very difficult to get enough people together to actually complete one, and it's going to take a long time to finish the "do 3" dailies. I prefer the Summerset model where there is often a low level elite at the end instead of super-tough boss, if there is just one or two players at the geyser.
Delves etc: VERY good. I love delve designs that have a lot of different paths and levels, and make it easy to get lost.
Exploring to find Collectibles: Middling. I like being able to sneak in and eat cheese at Giant's camps without necessarily killing them all. It's also cool finding various ancient nord temples in the wild. Vvardenfell (Morrowind DLC) set a really high bar for this factor though.
It really is good. I have gotten lost in just exploring. This will also be the first DLC/Chapter where I will be sad when my main finishes the zone and needs to move on. It's so fun.