I believe that Minecraft is the future of massive multiplayer games, and I'm surprised that none of the big developers/publishers have cottoned onto it yet.
They look at Minecraft and think its success is down to its business model, or to its blocky, retro charm.
It's down to the fact that you get out of it what you put into it.
With a MMORPG, there are pre-scripted quests. With Minecraft, you set the quests yourself or others.
User created content is the key. All you have to do is provide the players with the tools to build.
There are two types of gamer: wall builders and wall breakers.
Wall builders are the ones that spend an age in an RTS game getting their base just right. They play SimCity and act as Dungeon Master during an RPG.
Wall breakers are the type to follow the mission brief. They get set a quest and they follow it. They're the Call of Duty crowd and they're never more happy than when they're making progress through a game world.
If a title existed that allowed the former to create content for the latter to play through, with all the trappings of a big title like World of Warcraft, you'd have a killer game. One that would never run out of content.
They were talking about a possible online version of Fallout a little while back. My dream version of this game would be akin to Minecraft: There are no missions. You are simply ejected into the wasteland and told to fend for yourself. Players would gather to build villages and scour the environment for resources. Stories and narrative would be born purely of this player interaction, not pre-scripted missions.