Bump for much needed discussion at the early hours of the morning.
The appeal to WoW for me initially came when Jon (SG) introduced me to it back in August '05. WoW was just under a year old at the time, and I'd been hearing nothing but good things about it. On top of that, I'd always been interested in Warcraft lore since I'd played WC2, and he had a free account lying about for me, so I picked it up. WoW was my first MMO experience following Phantasy Star Online from way back in the day, and given that PSO was mostly "instanced" into small parties and lacked that true MMO mechanic, I really had no idea what I was getting into, but I've been more or less hooked ever since.
WoW is astonishingly simple in its game mechanics-- in fact, it's fairly bare bones compared to many of the RPGs that have been on the market, MMO or otherwise, but it's (I don't care what you nugz say) affordable and easy to pick up. Duckboy also hit the nail on the head: the game has more of a pseudo-fantasy atmosphere than a "ye olde medieval"-fantasy atmosphere. It's hard to explain without getting in-depth, but Blizzard effortlessly blends various types of styles that would usually be considered unique only to a specific genre (like sci-fi, for instance) into one giant fondue pot of eye candy and good gameplay.
The game can wear on you once you've logged enough time into it, and I have consequentially gone on hiatus from the game a few times now, ranging anywhere from 4-8 months, but it has a lingering allure that keeps the game interesting, whether for better or worse. More recently, Blizzard's made accommodations to the casual player for endgame content at level 70, as well as making the grind from 1-60 easier, so it's a great time to pick the game up and start playing if you've ever been interested before.