I liked the fact that npc's really got pissed off and would verbally tell you off. The gossip girls in recordists made for something unexpected in a game.
The interaction with your environment was one thing I loved with DD. Moving a bed to find a hidden trap door. Able to pick up someone's dinner off their table and use it to heal yourself.
For quests I fondly remember the vampire cave, lose some permanent stats to save a kid.
