Sandbox
From Neverend
It would have to be simple and complex at the same time. For example, it would give you the abililty to change the world, like create a bridge over a chasm that opens up a shortcut to a new zone, or enemy territory, but that would be interwoven with dozens and dozens of other features in the game. Players could easily figure out how to make the bridge or tear it down, and on a micro level, many players could be content with that. How long can you keep the bridge up on a certain server, for example? Or, can you make sure no one can build the bridge for an entire month? With dozens and dozens of features like this, maybe hundreds, players could amuse themselves with all sorts of player created goals, in addition to leveling, PvP, raiding, roleplaying, and all the rest of your normal MMORPG features.
However, on a larger meta level, the bridge could be just one part of a larger puzzle piece. Build the bridge, defend it long enough, that opens the possiblity of spawning a trading center, which is another dynamic feature requiring player actions. The trading center in turn, opens up the possiblity of establishing a city, which requires more player actions. And this whole chain creates one puzzle piece.
Complete another chain of dynamic features in the game, and you create another puzzle piece, and when you put them together, you are greatly rewarded. For example, you need to do another chain of dynamic quests to form another city, and when BOTH cities are in existance, they form a trade route, which opens up the possiblity of making seige engines, or something to that effect. However, losing one of the parts of the chain, like the bridge, could cause a domino effect, and the whole thing could fall apart.
While some players could have fun on the micro game, simply building a bridge, or tearing one down, other players would engage on the meta-level of the game, trying to organize guilds and players to accomplish much more complicated larger goals. However, players would absolutely NOT be required to get involved in that much depth, unless they wanted to. The casual player could just log on and do a quest, camp some Mobs, make a level. Or they could respond to an invitation to participate in some dynamic portion of the game.
The problem is still design. How do you make a world both HUGE enough to hold a large population, but make sure your population isn't so spread out the game feels dead? Bigworld Tech, as far as I know, can easily build a huge world: http://www.bigworldtech.com/index/index_en.php
Dark and Light used Bigworld, and the technology worked fine, but the design made it feel like you were alone in a huge world with nothing to do.
Darkness Falls in DAoC is an example of a Sandbox feature in a game. Players can battle over control of this dungeon, which actually changes the gameworld. Simply adding a few hundred, or even a lot more, features like this would make for a Sandbox game, no single server required.
