The thing that WoW has over pretty much every other MMO, and I've played most of them, is its elegance. Sure it's no gazelle,but compared to the butt-ass ugly and unintuitive interfaces of many of the other titles out there it's quite good.
Also, they're so much smarter about disguising grind. The busy work in WOW doesn't feel like busy work. There's an art to building a chain of tasks that are varied, challenging and entertaining enough that they don't feel tedious.
The interesting thing to see in WoW is the fracturing of the player base into core and casual gamer factions. After a year of playing you're seeing the people who want to spend all day in a raid instance butt heads with people who just want to come on, socialize and play some PVP and maybe try to get some loot. Many of these people are in the same guilds and I'm noticing a lot or reorganization, mass exoduses and mergers of guilds based on people's end game desires.
I can see the business fracturing in both directions. Game created for core guys who want to spend all weekend on team speak hearing their guildies succumb one by one to deep vein thrombosis and those more interested in role play, socialization and fun (guess which side I fall into).
