Key Features

Society - there is far more to this world than killing monsters and gaining experience. Many players might be more interested in advancing their position in society via their "fame". Earning fame for many players may be more important than earning experience or money. A player might want to marry a princess or other noble in order to gain even more fame (yes, weddings and marriages are more than just words - they are real in game events that adjust your fame and income).

Tight Economy - money will be critical.  There will NOT be a "player run economy".  There will be several money drains (food and shelter, equipment (wear out and require mending), supplies, animals, mercenaries, real estate, teleportation fees, stabling fees, dust of recall).  Vendors (NPC Merchants) will buy and sell items at +/- 30% of value.  Common "monsters" will not drop absurdly valuable items (ie an Orc Scimitar is not a good weapon).

Travel - there will be several means of travel - boats, horses, wagons, teleporters (getting together with your friends will no longer be a tedious task).
(initial release will only include standard foot travel)

Real Estate - players will be able to own apartments, houses, even castles (and will have to deal with the responsibilities - defending it, maintaining it).  Eventually players may even be able to design buildings! (initially we'll be swamped with the work of just creating the basic world and keeping it interesting but if you have a suggestion for a building feel free to send it in)

No spawn spots - there will not be clearly identifiable spawn spots for players to "camp".

Intelligent Monsters - foes will follow you anywhere. They may break off and flee if you approach a town. There are no "hard" zones (buildings and terrain will be loaded now and then causing some hesitations). There is no such thing as zone borders to use as a safety net (for protection against something that'll kill you, run back to guards... heh, this might take "days").

Unique Items - every item is unique (not a pointer into an item database). Certainly there will be duplicate mundane items such as a standard "long sword", but each item has the potential to be unique. Items crafted by players will be unique. Each time you forge a sword the attributes will be slightly different and you'll be able to name it.