As we tested out Quest designs we found two things were true, our quest were far more involved and interesting than other MMO games we'd played, and they still didn't meet our original design goals.
So we gathered some of our design team and had a multi-day intensive redesign of the entire system. I'm happy to report that our original goals are now met with the new changes to the system. We didn't get rid of anything we had before, we just expanded the system to allow far more player interaction.
Where before you would have had unique quests that tied into your story, now your actions during the quest have far greater impact on the quest as it develops and builds toward the climax... a climax that will be affected and changed by what you did along the way and what you do during the climax.
This new system also expands the quality and quantity of quests. This, of course, requires a redesign now of our quest building tool, and that is underway. More news on that later.