The hand-craftedness of morrowind. That was why is was so good. There was always something hidden. You saw the dev's hand in every area knowing someone would explore it even though it's off the beaten path. The vendors actually carried or stored their inventory and it could be stolen without some theft marker telling the guards across the world "this is Balti Ser's wooden fork, remove from player!'

Oblivion and later: paintbrush go brrrr