The final destination of the spirits of the deceased remains a mystery to the priests and philosophers of Azeroth. However, as spells such as [Resurrection] can reunite a dead body with its spirit, and a majority of living creatures from the tauren to the troll shadow hunters claim they can communicate with and call upon the power of the spirits, a widely held belief is that the spirits of the dead remain on the Material Plane — in an immaterial state that can only be altered or contacted through the use of magic.
It's hard to get a sense of an entire World of Warcraft expansion from 30 minutes of play. In my short demo, I recreated my main (a Beast Mastery Hunter) and played through the introductory quests from the Bastion zone, a heaven-like plane from Azeroth's afterlife. The minute-to-minute gameplay very much followed the formula of modern WoW questing, with a variety of tasks like challenging specific enemies to duels, helping craft things in timed minigames, and of course, killing 10 rats (well, not rats, but they might as well be).
The Shadowlands were originally intended to be a fully playable zone in World of Warcraft, designed for high-level play. The idea was that as deceased characters made their way back to their corpses, they'd see high-level players battling creeps in the area, which would inspire lower level players to increase their character level so they could experience the zone for themselves.
Explore the Realm of the Dead: for the first time ever in World of Warcraft, players will cross into the Shadowlands and experience the wonders and horrors of the afterlife across five new zones—the gleaming fields of Bastion, the scarred battlefields of Maldraxxus, the eternal twilight of Ardenweald, the opulent keeps of Revendreth, and the horrific Maw.