Well, I’m hoping that people learn the right lessons from World of Warcraft and, to a lesser degree, City of Heroes. I think those two are the most successful (in terms of quality, not numbers) MM games I’ve ever played, and the reason is that they’re games first, virtual worlds second.
City of Heroes is just Diablo with superheroes, more or less. And at least when I played, they put the focus on your hero’s experience, not on the idea of some virtual world. Having extra players around just fed into that, not the other way around.
World of Warcraft is deeper, but it’s still (as far as I’m concerned anyway, maybe my bias is showing) a single-player game that you happen to play simultaneously with hundreds of other people. They realized up-front that infinite content, world-changing events, enemies that die and stay dead, intelligent NPCs, and unlimited object creation, are all unfeasible. So they took the play mechanic and character classes of Diablo 2, polished the hell out of it, and set it in a virtual world.
There’ve been plenty of attempts to mimic a real world/galaxy/whatever by trying to give players to do whatever they want. And they all end up unsatisfying, because players need more structure than that. Games that have tried to have real-world economies have faltered because they overestimated people’s desire to log into a game and just be a baker or a dressmaker. Games that tried to force people to group together have faltered because of griefers and just plain annoying players. Games that have tried to offer both the crafting-only route and the combat-only route have faltered because neither one is completely fun and satisfying. And games that have tried to let players significantly change the environment have faltered because of jerks who power-level or camp or build wherever they want.
My ideal MM game would be predominantly instanced areas – not just dungeons, but entire zones – and the only areas where you’re grouped with everyone else is in the big cities or towns, which act as lobby areas. The instances could be tailored so that it’s a unique and interesting experience for you and your party, none of the waiting in line to kill the same infinitely-respawning NPC. You don’t need fancy AI unless you’re trying to provide infinite content, and you don’t need infinite content if each person or party gets his own version of the world.
The biggest problem to massively multiplayer games, apart from having too many people fighting over the same space and basically getting in each other’s way, is that there’s no persistence. Nothing you do makes a real difference, because you can’t permanently destroy or take over a town, you can’t kill anything without it respawning minutes later, and you can never really “win.” Having instanced areas doesn’t really address that – you could have a complete storyline within the instance, where you kill monsters and they stay dead, but once you got out of the instance, it would all go away.
I still can’t think of a way to set up an environment where what you do makes a permanent impact on the world, but still doesn’t have cases where months of development are ruined by the first power-leveler who hits level 60 in two days and goes and permanently kills the boss dragon. (I guess if I could think of a way, I’d be a pretty rich man.)