WoW was my introduction to MMOs, and ive never really replaced it, despite trying out ff and eso. That voids still unfilled, but I have picked up Warframe, which i suppose might technically count, but its not quite the same - third person mission based sci fantasy shooter doesnt quite scratch the same itch, but it is an mmo.
Great quests, i really enjoy them when they come in.
Labyrinthine progression system, im currently building a new class so that i can generate an Impact weapon and then i'll throw the class into the dumpster, absorb its power blue-mage style, slap it on a different class, and use an upgrade from another part of the game to turn that impact weapon into an energy generator, slap the ability on another class i like, and use the impact energy generator fueled ability to set up a whip attack that needs enemies affected by the blue maged impact energy weapon fueled ability to farm another - ok ill stop, but its this kind of game.
The space hats are good and pretty to look at. most important part imo.