The best game wolrds are the ones that you believe could go on existing if you as a player did not.

I think the pinnacle of this is probably Majoras's Mask. Link arrives after weeks of trouble for the inhabitants and the developers went to a lot of trouble to give them all different dialog, animations, routines and emotions over the 3 day loop the game is stuck in. Link of course manages to break the cycles by being the only person who can remember and uses this to his advantage in all the wonderful personal sidequests they all have, from the Deku scrub who just wants to move somewhere warmer to Anju and Kafei, gaming's greatest love story.