I'll humbly disagree. WoW is beyond succesful, no question there, but personally, I never thought it to be a good game. Things have changed since I tried it of course (at the BC launch), but looking at the critical reception, it seems to me that many critical issues (I consider them to be critical anyway) in WoW weren't solved until Blizzard let Deathwing fly a few weeks back.
Not to mention how the game basically caused MMO design to stall for a few years before everyone realizing that copying WoW was a bad idea, but you can't really blame WoW for that.
Either way, I would consider the game of the decade to be a game with compelling gameplay, and something that brings its respective genre forward and WoW hasn't done enough with either of those options in my eyes. It just made enough money to feed China for two years, and probably did anyway, one way or another. 
