Immersive World
Would like to see a realistic world where you can act freely without restrictions. Free in the sense of innovative forms of interaction with the world. Thievery anyone (skill challenge: target versus thief), climb anything, improved and complex crafting, pet, Eating, Sleeping, Farming, Breeding animals, fishing, hunting...
Government Structure
With a government structure interpreted by the players (judges, politicians and army). That would make a wonderful immersion. Imagine if a character kills another (PvP) and there were witnesses to the crime, would have to open an investigation into the crime and circumstances.
Death Persistent
It would be fun to see the monster rotting day by day ... I know there may be server overload and spoil the fun, but there was one more reason to work on character evolution. To protect low-level characters would PvP cities guarded by soldiers.