Yeah, I'm a junkie. My first MMORPG was City of Heroes, which I played for a couple of months, then stopped, then got a Mac so I couldn't play it anymore even if I wanted to.
Things that WoW does that I love:
-Gameplay. There's nothing so fun as pick pocketing a guy with my Undead Rogue, then Ambushing for a 350 hp critical hit, then building up another four combo points to lead into a gigantic Eviscerate finishing move of pain to finish the poor bastard off. All in about 10 sec. Likewise, Mages have big ol' Boom Boom spells, Warlocks summon freakin' demons, Hunters have trained tigers and whatnot to distract their enemies while they shoot the heck out of them, Warriors and Paladins are big damn tanks that can't be brought down without some serious hate, Druids shapeshift into whatever they need to get their job done...or just entangle the poor enemies and hit them with spells, and the Priests keep everyone else alive while using some nifty crowd control abilities (don't know much about shamans, but they're supposed to be pretty nifty).
-Interesting quests. In City of Heroes it was "clean up the streets" or "I need you to get random item X-312." In WoW there's more of a story to everything (in my opinion), at least I feel more involved than I did in City of Heroes. For example, my undead rogue has completed several quests designed to develop a new plague strain for which the undead can wipe out the humans and animate them to their own cause. Cool stuff.
-Death doesn't make me exit out in frustration. City of Heroes had XP debt, which just plain sucked. WoW just makes you run back to your body as an invulnerable and invisible ghost, no XP debt or penalty, just a minor hit to your item durabilities. Or you can choose to resurrect at the Spirit Healer and not run back to your body in exchange for a larger item durability hit and 10 min. of resurrection sickness (where all your stats are reduced by 75%).
-Interesting craft skills and player economy. My level 46 Paladin has made almost all of his armor and his badass hammer for himself, and it's all good stuff. I've really gotten a sense of accomplishment from getting that skilled at Blacksmithing. And it's nice how the professions require the fruits of other professions. My blacksmith Paladin needs leather for almost all of his recipes now that he's reached Artisan level, for example.
-Consensual PvP. At least on the PvE and RP servers it's consensual. And when you want to fight other players it's a hell of a lot of fun. Especially since their new patch reduced lag when multiple players are in the same area. And the guys who are good at it are REALLY good. There's a Horde clan on Feathermoon called Low Red Moon that has their tactics down cold! They pack the battlefield full of Alliance bodies despite being heavily outnumbered (multiple level 60s in their guild certainly helps of course).
-Relative lack of jackasses. Sure, they're there (and they're usually Night Elves), but mostly not. And the /ignore function or leaving the General chat channel deals with most of it. Oh, and ph34r, if you type in chat similar to the way you spell your user name, I'd rather sell you on not getting WoW...or at least not joining Feathermoon server

. If the name is a one-time leet-speak eccentricity though, Enduring Nobility on Feathermoon would love to have you (Alliance only, though a Horde guild may be forthcoming).
-Decent support from Blizzard. Sure, their official forums will tell you the exact opposite, but let me just say that when they were having HUGE server issues they extended people's free months by the number of days the game was unplayable. That's the right thing to do. They've also made some decent improvements over the course (and their upcoming developments look particularly good--a confirmation window for rolling on Bind on Pickup items for one).
Things I don't like:
-Blizzard's claim that the game is soloable from level 1 to level 60 is just not true. Even with my Rogue, one of the most soloable classes in the game, I'm getting more and more quests that I need help with. For my Paladin it's a necessity to group. Granted, I group with good people, but I like the autonomy that soloing gives you.
-Population issues. The RP servers are overcrowded, though now that they've opened up two new ones I'm hoping the problem lessens. Also a problem is how the Alliance outnumbers the Horde by a fair margin on almost every server--this makes elite squads like the aforementioned Low Red Moon a necessity for the Horde. My advice is to pick a server (if it's not Feathermoon) that has a Medium population at peak hours--not so large that you're overwhelmed when you visit Ironforge or Orgrimmar but not so small that you can't get the one item you need to craft a recipe or complete a quest from the Auction House.