Have you seen Gawain’s mmorpg Manifesto? He brings up some very good points and I think anyone that is interested in this kind of game should read his post. The growing list of what should be in a mmorpg is something every developer of these games should be emailed. Feel free to email G with suggestions if you think you have something that needs to be added to the list. Be prepared and have a good reason why your thing should be listed. G is awfully opinionated about these games, as we all are. Here are the first 5 on his list (to bait you into going to his site):

1. A 100% player-driven economy. NO npcs, except for possibly quest npcs, though only on a very limited basis.

2. A Dynamic landscape. The lands that the game takes place in MUST BE ABLE TO CHANGE EASILY. Trees must be able to be cut down, rocks must be able to be moved, and the landscape must be able to display damage. (from say, dragon fire or cannon shot)

3. The land must follow real-world physics and cycles, and must be affected by them. When it rains, rivers and lakes rise. It becomes more difficult to walk on bare land, as it becomes slippery and muddy. When it snows, the rivers and lakes freeze (or CAN freeze) allowing characters to walk on their surfaces. After rain, fog must form above bodies of water, limiting visibility. Lightning must be able to strike tries and tall buildings, as well as characters (though the chance can be obviously low).

4. Day, Night, Seasons, and other special conditions must have a real impact on characters. In the winter, characters without adequate clothing must slow down and eventually freeze, unless they find a heat source quickly. Rain must lower visibility, as must nightfall. If it rains blood and meteors, characters must be able to be damaged by falling debris.

5. Players must be able to have an effect on the game world. Players must be able to construct buildings anywhere they please, provided they have adequate materials and time, and the ground is reasonably flat, and they have the required skills to do so. Players must be able to chop down trees, haul lumber, and process minerals, etc etc.

Credit for the above list of course goes to Gawain. I had a small hand in the tweaking of number ten. And there has been a number of excellent suggestions from Doom.