Just being a persistent world was a huge novelty in and of itself.

Asheron's Call was my time sink. It had quests and stuff but the devs had a storyline they developed with active monthly updates. It made everything feel so alive on top of it also just existing in realtime.

And even so the quests and stuff they added was extra fluff. The social system and trading economy were the backbone of the game. It wasn't until trade bots really took over that the social system collapsed.