WoW is extremely popular based on the fast it is very easy for a new gamer to learn. It's the perfect introductory to gaming. It's easy to understand, everything is laid out for you and the quests tell you exactly where to go. It's more solo friendly than it is group friendly, so for those learning, or who dont have time to get a group together, it's the perfect set up.
But for the gaming community at large, EQ2 has it beat hands down. If you are already familiar with MMOs, this is the perfect combo. You have both solo and group stuff. More is based on group, but there is no way you couldn't get to lvl 70 soloing. Its been done and often. The quest lines have a real good story to follow and they get you involved. There's more of a community feel to it, not every man for himself, as most people do enjoy grouping together. You have guild levels as well, which helps those in guilds really want to work together for the good of their own guild and get it high for the rewards.
And unlike WoW, every class really is desired, and SOE is trying to make it even more true, with the recent addition of raidwide fighter buffs. I remember playing a hunter in WOW and knew full well once I hit cap level I would pretty much be done. And it was all because of the class I chose to play, not because of how good or bad I was as a player. There is no room for hunters in raids. But EQ2 has room for any class, as each one brings something special to the table which enhances raidplay.
I love both games, and I've been known to switch from one to another once in awhile, just to get a fresh breath. But I always invariably come back to EQ2. I've met some of the most amazing people there, and I enjoy having a bunch of friends where we can get together casually and go raiding. You dont have to be hardcore to see end game. You just have to know your class, what other classes do, and find a good guild of people.