What comes to mind is, what really tickles your fancy? What is it that draws you into a game and keeps you playing. These can be tough questions when it comes to an MMO because of the longevity of the game and the fact that the game never truly ends.
So with knowing that, what is it in an MMO that has no end game cut scene that truly draws you into the game and keeps you playing it for years.
Feel free to reference other games that kept your attention and focus on the details. This should be a great resource for dynamite to see what they need to focus on to keep attention.
I'll start and say that my favorite memories of games of old was the need to find other players to accomplish almost impossible tasks. The feeling of spending days working on something to finally see it through was a rush that kept me motivated. That coupled with the myth of items that I may have seen a few times, achievements, areas that most people couldn't get to, keep me going. I love to step ahead of other people and do things most people say are impossible. I would gladly smash my head on something 1000 times if one of those times I learned one small thing and progressed.
My psychology is a man of detail, and progression on even the smallest scale. Something a casual player would never notice. Those are the things that fuel my need to play.