10 levels of lore packed questlines. Approximately 80+ quests comprising the major lore of a zone, with 20+ quests for various other lore. Like Horde in Nagrand.
I'd also like to see dungeons, raids and scenarios to have some kind of prequest(-line) before you can enter. With followup quests inside that tie the overall lore of expansion/continent together.
For example in Vanilla Blackrock Depths was tied together with Upper Blackrock Spire through the Onyxia attunement quest.
Upper Blackrock Spire was tied with Lower Blackrock Spire and the area near Onyxia for the entrance quest into Upper Blackrock Spire.
The Onxya attunement quest also took you all over the world introducing you to the 4 dragonflights other than Onyxia's Black flight.
Blackrock Depths was also tied to Molten Core through an attunement quest.
Molten Core was in turn tied to Blackwing Lair through the questline for Thunderfury.
Blackwing Lair was also tied to Onyxia since you needed the Blackflame Cloak to protect you vs certain bosses
The boss of Blackwing Lair, Nefarian, and Onyxia are also siblings.
The moment you set foot in Blackrock Depths, you were in for a long and epic ride on the rollercoaster of lore all over the world. I miss that kind of connection between places.