A game in progress is a fluid thing. A game mastered is… what? The typical answer to the endgame, at least on the MMO scene, is raiding. But not everyone is a raider, and raiding was only a fraction of the gameplay up until the end. What can solve the endgame problem for MMOs? Gamasutra has the story.
My solution would involve minigames that tie into the social and political fabric of the game, or which have to be repeated to maintain a character’s place and possessions in the world. Sort of a combination of Harvest Moon and Sid Meier’s Pirates. Always something to do, and always a reason to do it.