A lot of focus on player to player interactions due to lack of GM unlike a table top session.
And this is why the MMO concept needs to be abandoned in favour of a MUD/CRPG creator hybrid. NWN with a capacity for several hundred people per shard/PW. Let the players take up the slack of creating and running content. Make it easy to GM 'modules'. Do all this and they will beat a path to your door! Xryptic was on the right track - sorta kinda - with Neverwinter Online, but their acquisition by Perfect World has ended any hope of that. I'd really love to see Obsidian make something like this. You could port any crpg to it, D&D, WoD, Pathfinder, GURPS, etc.
"I like my coffee like I like my women. Black, with a side of prune danish." - Gilbert Gottfried