If I had a double bacon cheeseburger for every forum post titled "Why do people [still] play World of Warcraft?" then I would have died of a coronary a year before The Burning Crusade went into beta. Now, mostly these posts are from basic internet-level malcontents and trolls, or people who can't grasp the idea of different people having different personal tastes. But I want to take the question seriously for a minute, partly so that you can just drop a link to this article the next time one of those threads appears, but mostly because I think that hopeful MMO game designers might be asking themselves the same thing.
Ten million subscribers. At $15 a month each, that comes to $150 million a month and 1.8 billion a year. If you could capture just one in ten WoW users and get them to jump to your MMO, you'd be a massive success by industry standards. I know you want to. Here is my advice for the next developer who comes along with a head full of ideas and dollar signs in his eyes:
Broad System Requirements
The WoW juggernaut proves that graphics take a backseat to gameplay for most players. Your game doesn't need to look like 8-bit warmed over, but it does need to scale down gracefully to the low end of the spectrum if you want to take a bite out of the WoW user base. Yes, sexy screenshots help at launch day, but if the game looks wrong and runs slow on the average machine then you're destined to be a minor player in the MMO world.
MMO games are social by nature, but WoW benefits a great deal because people join simply because that's what all of their friends are playing. Stomping around Northrend with your friends is a perfectly legitimate way to spend an evening. You can joke and gossip and bitch about work and school while sitting around your favorite restaurant, or you can have the same conversation while fighting a Flesh Giant or traversing Zul'Drak. I know the average MMO looks like an RPG with a chat bar, but there's a lot more going on here than just chat. If you want to knock WoW off its perch, you need a way to make that Northrend conversation as seamless as possible. You need to give players lots of tools to acquire and connect with friends while filtering out irritants and idiots.
People dismiss WoW as a "mindless clickfest" but the truth is that the game is not multiplayer Diablo. The game feeds you new combat abilities at a steady rate, so that a new one opens up just as your existing skill set is starting to feel a little tired. There are a lot of different enemies that require different approaches. The combat will get old eventually, but for people that like combining powers and experimenting with different character builds it can offer many hours of entertainment. Your upcoming WoW-killer needs to be able to offer a variety of combat experiences, from complex hot-key driven action strategy (Rogues in WoW) to casual point-and-click for people who like to play while watching American Idol. (Hunters in WoW.)
What few MMOs seem to grasp is that being able to walk from one end of a massive gameworld to the other is deeply satisfying to people with a sense of wanderlust, and the effect is often ruined if you break the world up into little playpens connected by loading screens. WoW has many different areas with unique music, mood, lighting, monsters, architecture, cities, wildlife, and flora. There is a ton of content to consume here, and lots of players derive satisfaction from taking the world tour. The game creates the impression that there's always another cool landmark or impressive vista just over the horizon. If you want people to stick with your game, you need to give them stuff to look at. A lot of stuff. It's not about square mileage, it's about seamless variety and spectacle.
The idea of traveling a gameworld and picking up stuff has been with us more or less since the dawn of gaming. Maybe it's our hunter-gatherer instincts. Maybe we just like finding treasure. Whatever the reason, people love acquiring great big heaps of loot, and WoW has a large number of ways to do that. Gathering herbs, mining, fishing, and skinning are all ways to line your backpack with cool stuff without ever needing to fight anything. The treasure is just laying around the world and all you have to do is get out there and pick it up. You need your game to entice people to play it by drawing them into the wilderness with a trail of useful resource goodies.