Watching the dwarf character running (and its other animations as well).
The Quests; the need to discover and understand the settings, sustained by the quality of the settings.
The quantity of small interactions you can have with living characters. One day encounters, new faces running around all the time, living their lives (and not there to whack you on sight, which is fun, but in another kind of games).
The variety (races, skills, activities, places, play styles, ..., and growing).