My quick list during a late lunch break:
- Slow experience (slower than live).
- Indepth quest lines that provide immersive background flavor.
- Combat that is less twitch flavored and more strategy. (and not the "move here for 10 seconds, then move here for 15 seconds" types of "strategy")
- Interconnection of zones in an unfamiliar fashion. (such as SoD)
- Less gear dependency.
- Ability to customize classes to playstyles. (this could be as simple as only giving certain spell/combat skills after completing the quests -- which might preclude you from gaining another type)
- Real storylines. Ones that provide context and are dynamic to development ideals.