I finished the death knight campaign from Legion last month, and it was as excellent as I heard. I know this is content from last expansion, but I should note that this post will have spoilers.
Over the course of the campaign, the Knights of the Ebon Blade work with Bolvar, the new Lich King. In exchange for the Lich King directing the death knights to two artifacts, helping with the third (reforging the shards of Frostmourne into the twin Blades of the Fallen Prince), and keeping the Scourge contained, the death knights agree to act as Bolvar’s vengeance against the Burning Legion. Bolvar asks the Deathlord, the new leader of the Ebon Blade and the player character, to raise new Four Horseman.
The first, Nazgrim, is my favorite. I loved Nazgrim. Seeing him develop from a Sergeant in Wrath to a Legionnaire in Cataclysm to a General that we defeated in Mists was a great experience that made the world feel much more alive. Plus, he’s responsible for “Thrall’s balls!” And now he’s one of the Four Horsemen.
The second is Thoras Trollbane, who was a king of Stromgarde. Honestly, I don’t really care about this much.
The third is Sally Whitemane, who was High Inquisitor of the Scarlet Crusade. This is another cool callback.
Finally, Bolvar sends the Knights of the Ebon Blade to Light’s Hope Chapel to raise Tirion Fordring as the leader of the Four Horseman.
In the finale of the campaign, the death knights invade the Sanctum of Light, a secret underground order hall beneath Light’s Hope Chapel. It serves as the paladin order hall for the Knights of the Silver Hand, although the scenario is instanced so you don’t see players. After defeating Lady Liadrin, the Light itself stops you from resurrecting Tirion. Highlord Darion Morgraine uses a deathgate to escape but is killed in the process. Back in Acherus: The Ebon Hold, you resurrect Morgraine as the fourth horseman.
This was a fantastic finale to the campaign, and I loved experiencing the darkness after playing through the priest campaign. The priest campaign was really boring, and it never really felt like we did anything cool. In fact, the end of the priest campaign had the order hall, Netherlight Temple, get attacked by a dreadlord and the Knights of the Silver Hand come to save them. I like kicking some butt as a death knight over getting saved by the paladins. Although now that I think about it, I guess the paladins were the ones who really won!