I'm mostly a fan of single-player games and don't feel that massively-multiplayer games can come close to offering the same level of engagement or fulfillment, apart from the social fix.

The biggest concern I've had against investing emotions into any MMO's content, is the complete lack of a guarantee that it'll always be officially available. So many quests and such get old pretty fast and eventually forgotten. There's just no way to relive that content.

Maybe a paradigm shift is needed, away from how MMO content has been traditionally designed.