The quality of the text associated with quests is one of the major criteria upon which I judge an MMO. I don't mind killing ten rats, as long as you give me an enjoyable back-story to justify it. The better MMOs will even communicate the lore of the game and set the tone of an area using quest text. For example, this text from a recent Allod's Online quest really jumped out at me:
"You know that creatures have arms made up of bones, muscles, and tendons, all dressed up in a flashy covering of skin? But what's the use? What's the use if they break and tear so easily? We Arisen, on the other hand, have much more practical arms made out of sturdy metal."
The Arisen are essentially undead cyborgs (think a Renaissance version of the Borg from Star Trek the Next Generation and you will be on track) . The text from that quest does a really good job of conveying the disdain that the arisen feel for most of their allies, and just how generally odd and creepy they are.
It's a lead in to a fairly standard "gather X of Y" quest. However, it also communicated something important about the setting of the game. That is a quest worth doing and reading in my mind.