But with every year that passes, the pressures on it increase - from big-ticket rivals like Star Wars: The Old Republic, the busy gaggle of free-to-play games, and from untamed community hits like League of Legends and Minecraft which seem to be able to summon tens of millions of players out of nowhere.
Nevertheless, WoW's greatest enemy by far is itself. Or, perhaps, it's its age. It's been a long time, now - for all of us.
The efforts of Blizzard's developers to stop the clock from ticking have been heroic. They've constantly refined the mechanics and the storytelling while decorating an ageing engine with an astonishing volume of beautiful and lively artwork. After bringing WoW to its creative peak in the second expansion, Wrath of the Lich King, they somehow summoned the will to redo the entire thing to the same standard in last year's Cataclysm - a colossal work of revisionism that stands as a unique achievement in video game history, and probably will do for some time.
But even that couldn't defeat the passing of time. After ravenously consuming the new and revamped content, WoW players hit maximum level again, started queuing for their rations of advancement again in battlegrounds and raids and dungeons, and the familiar grind finally got too much. Their discontent was voiced in yet another round of whining about raid difficulty (too hard, this time) but that was just displaced ennui. They didn't want to admit to themselves, or Blizzard, that they were bored.
So the reaction to next expansion Mists of Pandaria, unveiled at BlizzCon this weekend, has largely been surprise and bewilderment. It features a new playable race of kung-fu pandas, the Pandaren, running around a cartoon version of ancient China punching rabbits and monkeys. There's a pet-battling mini-game that bears a striking resemblance to Nintendo's Pokémon and a radical simplification of talents, a cornerstone of the game's class design. This is Blizzard's reaction to unrest amongst its most dedicated players? This is going to keep the game at the top?
The first clue: there's no big bad. No monster or villain has been summoned from Warcraft's bulging lore books to threaten the world, lure players on a charge into unconquered lands and inevitably turn up as the final raid boss. That's extremely telling. World of Warcraft's dungeons and boss encounters have been at its core since day one - but at the highest conceptual level, Mists of Pandaria just isn't about those fights any more.
They'll be there, of course: three raids at launch, six new dungeons, and Heroic-level updates of classic encounters Scholomance and Scarlet Monastery. Outdoor raid bosses freely roaming the game world will also make a welcome return. But at a story level, the real fight is a different one. Blizzard's head writer Chris Metzen said the true enemy in this phase would be "war itself. [Horde and Alliance] are going to get it on with a level of ferocity that has not been seen since Warcraft 2."
It's the long-promised, never-realized dream of a game that, while being built around the theme of racial conflict, has never excelled at large-scale player-versus-player warfare. But there's no promise at all that this war will be realized in game play terms in Mists of Pandaria. Metzen calls the new continent of Pandaria "the calm before the storm" and the only PvP features discussed are a new Arena and a few admittedly intriguing Battleground variants, including one that puts players on the ground in a version of the famous Warcraft 3 mod DOTA.
So no, WoW isn't about to turn into a PvP monster overnight - not yet, at any rate. But, thematically, Mists of Pandaria is taking the interesting step of making the very factions the players belong to the villains of the piece.
As you explore Pandaria, a land that's lain hidden for 10,000 years, you will encounter not just the noble Pandarens but a number of other indigenous races. Seeking to exploit Pandaria for its resources, the Horde and Alliance pick sides with some of these and stir up trouble between all of them. The strife you're trying to solve is your fault in the first place.
Metzen recently told me that he sees WoW as "a study of societal breakdown and why do we keep clobbering each other, why does hatred persist generationally?" Mists of Pandaria's message doesn't sound anti-war so much as anti-colonialist, but either way, it's a surprisingly philosophical theme for an expansion that, on the surface, has a very light, comic tone.
Mists of Pandaria is more sober than it seems. The sense of fun is obvious and quite intentional, right down to the pot-bellied lope of the Pandarens' run animation. But, playing the entirety of the Pandaren starter area up to level 10, I'm surprised to discover that it's played quite straight, with the comedy mostly gentle and character-based - whereas Cataclysm, despite its apocalyptic theme, often went for broad satire, surreal silliness and knockabout slapstick in its quests.
Starting a Pandaren character, you join a Pandaren tribe that lives on the back of an island-sized ocean-going turtle called Shen-zin Su. You study the martial arts with an aphorism-spouting tribal sage (the writing is wonderful) and help to bring harmony to the environment by reuniting four impish elemental spirits in a great temple. On your adventures, you spend time with gently bickering chalk-and-cheese heroes Aysa and Ji, and see your wise old master laid to rest.
Then a memorable hot-air-balloon trip to the turtle's head reveals that he is suffering from a "thorn in his side"; it's an Alliance ship (with Horde prisoners) wrecked on his shell, and they've brought sea monsters with them. After cleaning up the mess, you're given the option to join either faction, a first for any race in WoW.
China has strict rules about the representation of the panda bear, which is revered in its culture. After the bureaucratic roadblock Blizzard faced in China regarding Wrath of the Lich King's undead theme, basing an entire expansion around the adventures of comical anthropomorphised pandas in a cartoon kung-fu wonderland initially seems suicidal to the game's success in the country.
"Perhaps it is a sign that Blizzard has one eye firmly on its growing audience in the East."
In fact, it's quite the opposite. The Pandarens are represented as a philosophical, noble and good-humoured people who participate in conflict through a sense of honor and adventure rather than bloodlust. The music is pure Crouching Tiger and the stories tip the nod to the balanced mysticism of Eastern myth. There's surely an extent to which this expansion is for Chinese fans.
"I think that definitely it's an opportunity to inject some Chinese culture into the game, and I think that that will be appreciated out in China," Blizzard's president Mike Morhaime says. WoW wouldn't be the first MMO to try to curry favour with Asian players this way and perhaps it is a sign that Blizzard has one eye firmly on its growing audience in the East.
There's another side to Pandaria's lyrical mood, though. It's more reminiscent of the measured unfurling of the Nordic continent of Northrend in Wrath of the Lich King than the disjointed fantasies of The Burning Crusade and Cataclysm. Lead designer Tom Chilton speaks about wanting to "get people back into the world". "I don't know about you, but I'm getting tired of seeing the inside of Stormwind and Orgrimmar, queuing for stuff," he says.
Like Cataclysm, Mists of Pandaria will present five large high-level adventuring zones spanning five levels (the level cap will be raised to 90). But like Northrend, Pandaria will be a contiguous and coherent landmass rather than a series of showy ideas. You'll see rice paddies, coastal jungle, great breweries (the Pandarens like to eat and drink), elegant temples, lush rainforests and stone spires.
Questing through this land will be emphasized at the endgame as well as during levelling, and the idea is that level 90s will have many more options for progressing their characters than PvP, dungeons and raiding. Every activity will award the Valor Points used to buy the best gear in the game, including questing and the new scenarios.
Scenarios are one ofthe most interesting developments in Mists of Pandaria: the sound bite is that they're "PVE Battlegrounds", and they seem to be the public quest idea from Warhammer Online and Rift crossed with Lord of the Rings Online's Skirmishes. Seen as a replacement for group quests, these mini-adventures are multiplayer, multi-stage dynamic events which can be played by any assortment of characters - you won't need to form up with tanks, healers and damage-dealers. They'll be instanced, and there'll be a queue interface for them much like the Dungeon Finder.
Between scenarios, much more questing and the amusing but surprisingly deep pet battles, Mists of Pandaria will have a lot of options for the endgame player who's tired of the raid treadmill, or scared of it. Meanwhile, hardcore dungeon fanatics will be catered for by a sporting new Challenge Mode.
Challenge Mode is comprised of dungeon time-trials inspired by the "45-minute Baron run" in the classic Stratholme instance. In these, you'll aim for bronze, silver and gold medals, visually striking armor sets, and most importantly bragging rights on leaderboards; crucially, a system that automatically normalizes your equipment to a predetermined level will ensure the playing-field is level and the focus is on player skill and teamwork.
Mists of Pandaria is currently least convincing, surprisingly, in its biggest new feature. The new monk class is a hybrid hand-to-hand melee fighter and can be specialized to tank and heal as well as do damage - although even the healer will supposedly be capable in combat. For the first time in WoW, the class has no auto-attack; every strike is a key press.
It's a mouthwatering prospect, flexible and dynamic, and the animation is fabulous. Some skills, like the long-range flying kick opener, are great wire-fu wish-fulfillment. But over those first ten levels, the Monk doesn't really hang together. Its resource system is muddled and, rather than flowing "like Street Fighter" as the developers intend, the real-time combat rotations feel forced, wearisome and lacking in tactics.
Variety and refinement will no doubt come with more development; Blizzard hasn't made a duff class yet, so there's no reason to assume it will start now. Similarly, it's likely that the new talent system will offer elegant simplicity rather than crude dumbing down, even if the intention that it will banish "cookie-cutter" character builds forever is probably too much to hope for.
But this WoW expansion isn't really about the big changes and box-ticking bullet points of new race and class. Challenge Mode aside, it's not about the dungeon-crawling endgame either.
It's about something that WoW offered with rude brilliance in its original release, and later perfected in Wrath of the Lich King: adventure and exploration. The discovery of an extraordinary new world with thousands of other players by your side.
It's an expansion for Asia, certainly, but it's also an expansion for the silent majority of casual WoW players who always preferred exploration to poring over stat sheets. Maybe Blizzard feels that the hardcore has started to slip away from it and that WoW's future lies elsewhere. Maybe it's right, and this artful and fun expansion will refresh the game all over again.
But even if that proves to be beyond it, you shouldn't worry about the pandas and the Pokémon. Mists of Pandaria is not the shark-jump it looks like. WoW's best years may be behind it, but it's growing old gracefully.