The problem with MMORPGs is that everyone wants to be the hero impacting the world. It's not too fun if you're just a cog in the machine, told of the glorious deeds of others. You'd rather be the one to swoop in and save the princess, or defeat the invaders, or thwart the plan to conquer the galaxy.
How does a game designer make sure everyone has their moment in the spotlight? How does he make every single player important enough so that they not only enjoy themselves, but also throw money at him? This is pretty easy to do with theme-park MMOs; just build the raid roller coasters. Unfortunately, the world ends up being pretty static as a result. Every update cycle, the players might get a new ride, but they are powerless in influencing the course of events in the world.
How does a game designer make sure players can change the world? They create the tools necessary for players to fight each other for land and resources. One guild becomes the invaders, one becomes the evil empire, and another, the good guys. Unfortunately, only a handful of players are at the helm. The average player isn't the one to save the world; he's just a peon in the plan. The world might change, but the player himself did very little to make it happen.
Designers (and critics) have traditionally seen the player-hero and dynamic-world characteristics as trade offs--as being mutually exclusive. Games are either hero-centric (theme-parks) while giving up world dynamics, or they are dynamic (sandboxes) while giving up hero-centricity. What if this was a false dichotomy, and we can actually have both? Everyone is the hero (or villain) saving (or destroying) the world. A goal should be to make one player the center figure in a story told by another player.
You start by encouraging players to make factions/guilds. The more guilds there are, the fewer players are in any one of them, the more responsibility each player has within that guild. They should also be extremely easy to create. Any group of players from anywhere at anytime should be able to found a guild. No purchase necessary.
Whatever sort of combat is in the game, it needs to be small scale (or to encourage small scale if it's mostly open-world combat), so that each player contributes more and can more easily "save the day". If players die, they should be able to spectate the rest of the battle.
There needs to be NPCs, all of which are completely Common. There can be no desirable attribute about any NPC. No Emperor. No Robin Hood. They are all peasants who need the adventuring players to save them. All of whom grovel at any player who walks by. Whether or not these players actually did any worthy deeds, they are still heroes in the eyes of the NPCs. This illusion is paramount. There should be no "prove yourself to me, private!" or "go talk to the General; he has orders for you".
If guilds can acquire land, then the map of the world should show everyone which land is owned by which guilds. Guilds should be able to designate how their architecture looks in style and color. They should be able to change environmental effects on the lands they hold. E.g. lighting color, weather effects, musical ambiance. Guilds should not only have a political influence on the world, but they should also have a visual influence.
Allow market monopolies. Sure they might be detrimental to the economy, but if players can only get their Zoonie-wigs from Xxpinkponyxx, then that player has become much more prominent in the game. (And if Xxpinkponyxx is charging and arm 'n a leg, perhaps she might get pushed around a bit...) Regional resources are an easy way to accomplish this.
You can give a little guidance to guilds. Perhaps send the guild leader a mission objective once every 3 months. In it, have dynamically generated quests which look similar to Risk's mission system. Make guild SuperMen conquer some land owned by guild Umbrella. Require a guild to get 3 other guilds to declare war against a land-holding guild. Ask a guild to own x square miles in land or a certain region. Amass a certain number of members or resources. Once the guild completes the mission, prominently display the guild and some featured members (those who contributed the most to the mission) where everyone in the game can see. Make those lowly peasants talk about the players and guilds.
These are some very abstracted ideas, and implementation details will vary. Give players the tools to influence the world and some place where they can show off. But make sure there are small pockets of communities. A hero doesn't have to be the one to throw the Ring into the fires of Mount Doom or the one to free everyone from the Matrix. He just has to be the one people tell stories about.