I played World of Warcraft quite a bit over the last two years, although I've given it up in the short term in the best interest of finding a job (generally an important thing to have!) While WoW was enjoyable to play, and well crafted (I actually appreciate the stylized artwork, although I realize not everyone does), I didn't feel that it offered enough redeeming features. While games are, for the most part, for recreation, I think that they should challenge the player in some way--either through hand-eye coordination, strategic thinking, or diplomatic ability, etc. WoW doesn't really challenge either--the only significant skills it builds are planning and working toward achieving goals. Galactic Civilizations II offers that as well as significant challenges to strategic and operational thinking.
What I'd really like to see would be a massively multiplayer strategic game, but there are massive design issues there yet to be resolved. Many people who play strategic games like to do so for the "emperor of the world" feeling--that's easy to do with single player games, but when there are a thousand players, only one of them can be emperor, and the rest will be left wondering why they're playing the game. That's a fundamental challenge to the design of an massively multiplayer strategic game, so I don't think we'll see a good one for quite some time, if ever.