In World of Warcraft, Blizzard hasn't reinvented the wheel for Massively Multiplayer Online Role-Playing Games (MMORPGs). Agro, tanking, mobs, grouping, phat loot and all the other MMO building blocks are still here. It's just that Blizzard figured out what causes people to get tired, bored and complainy and tried to do as little of that as possible. The game is super-fast paced; you're always on the move and the streamlined quest system means you're never lost, confused or strapped for something to do. The class choices are a bit smaller than some other MMOs, but each class is versatile and distinctive, and even traditionally "dull" classes like priests are given a wide range of unique skills that make them nearly as viable as mages. Professions strike the perfect balance between complexity, utility and fun.
The art direction is masterful, reliant on colour schemes, animation and shapes rather than just jargony techniques and polygon counts. Each area and central city has a distinct flavour, from Thunder Bluff's soaring mesas to Ironforge's central lavafall. Instanced dungeons - giant private areas created especially for you and your party, that house serious uber-quests - are the game's mini-masterpieces, with fantastic enemies and creative design that makes dungeons in other MMOs feel like amorphous lumps.
The game itself isn't flawless, nor is it technically finished - a good many quests fall into a "kill 20 of enemy X and collect nine of item Y" pattern, a lot of promised end-game content still isn't in, and there are still bugs being squashed - but it's easily the closest MMORPGs have yet come to perfection. If this one doesn't hook you, nothing will.
Visuals: Superb attention to detail for the environment, a great trade-off for the average character models
Audio: Excellent audio cues highlight key moments, integrating nicely with gameplay
Gameplay: Very addictive, a virtual time sink