Just because WoW has the most players doesn't necessarily mean it's the best, just the biggest. Personally, I found the lack of things to do at 80 a major flaw. I don't have an active sub now, nor do I intend to return for Cataclysm.
For me, it's City of Heroes. Create just about anything in your head, and you can build a character that atleast embodies the concept. Tons of story arcs, random missions for quick EXP, and now it boasts user generated quests as well. Also, thanks to the nature of powersets, two characters of the same archetype don't play the same. A Dual Blades scrapper is much different than a Dark Melee scrapper. But, there is a grind at post 35. Takes forever to get the next 15 levels, which is what drives most new players away.
