WoW was accessible in a way that previous MMOs were not: instead of repetitive grinding from the very start players are hand-held through levelling with the quest system and a story line. The levelling dungeons have comparatively generous static loot tables, with the rare drops from those dungeons just a nice little bonus. It's not until endgame that WoW reverts to genre.

WoW IMO killed Star Wars: Galaxies, which was exploring a more "open world" style of game; subsequent expansions progressively dialled back the classless system and player generated content.

More traditional repetitive grind MMOs remain popular in some parts of the world, but it's either EverQuest style or WoW style MMOs now.