Frankly, the aspect of Shadowlands I'm most excited about is an overhaul of the leveling system—something that wasn't a part of this demo in a major way. This kind of breaks the rules of a hands-on article, but I want to take an opportunity to talk about it and why I think it's interesting, regardless, since it came up in my interview with WoW developers.
Beings of death are ancient and powerful, and it is dangerous to meddle in their realm. When Odyn peered into the Shadowlands, he saw some of its inhabitants: souls in torment, the husks of the dead, ghostly wraiths with no face, and others with no form, all made of death itself. This was enough to frighten even him. Several races in the Shadowlands, such as the kyrian of Bastion, are souls of deceased mortals who have been transformed to serve a new purpose. If one of these former mortals is killed in the Shadowlands, they die permanently. Other creatures—such as dredgers and stewards—are endemic to the Shadowlands and are naturally born from the magic of death to serve the different realms and help facilitate the process of the afterlife. If one such creature of death is killed, their energy is recycled back into the Shadowlands, and eventually another member of the same race will manifest to take the place of the one that was killed.
During the Burning Legion's third invasion, the Knights of the Ebon Blade traveled to the Shadowlands to acquire the Aggregates of Anguish, five tormented essences of powerful souls - Admiral Proudmoore, Soulbinder Nyami, Grand Empress Shek'zeer, Grand Apothecary Putress and Archmage Arugal. Salanaar required these to conjure the Steeds of the Damned for the order's new Horsemen.
Blizzard hasn't talked about what it plans to do after Shadowlands. I speculate that the longterm solution would be to do this every expansion—so in the next expansion, Blizzard might move Battle for Azeroth into the multitude of choices for new character-leveling experiences and push level-cap characters back down to 50 to start whatever expansion comes after Shadowlands—an odd hybrid of traditional MMO and a seasonal model common in plenty of modern multiplayer games.
Ascend the Tower of the Damned: at the heart of the Maw lies Torghast, Tower of the Damned, a cursed otherworldly prison where the wickedest souls in the universe are locked away. Highly replayable and inspired by roguelike games, heroes are invited to explore its ever-changing halls and chambers and do battle with the minions of the Jailer, Torghast's vile ruler. Those who brave its trials can claim legendary treasures and help free the heroic spirits wrongfully trapped within.