Well, I've been thinking about how to make more involving, 'epic'-style quests, but I just can't seem to come up with any that doesn't involve things changing (NPCs dying, portals opening, gods' avatars appearing, villages burning, etc.). The problem with that is, only the people who have taken the quest would be able to see the changes, which would be just weird.
So, the only way I can really see it working was if some of the more important, 'epic' quests took you to an instanced location (i.e. each person or group gets a version of their own zone). That way the quest can facilitate things like NPCs (that you meet in the instanced zone, and nowhere else) dying, or other changes that wouldn't effect the outside, non-instanced world (you could even have cutscenes this way).
Anybody think this would be possible?
(Note this is different from the topic of instanced dungeons, which is really just to avoid kill-stealing...)