[Intrepid Homoludens]

By idle animations I meant that whatever characters/creatures/flora do on their own when you're not interacting with them. For example, two NPCs carrying on a conversation until you come up and ask them for directions. A flock of birds feeding until you approach and they fly away. Even things like smoke billowing form chimneys, insects, and passing clouds.

Sound is also a crucial element. I remember in realMyst how alive it felt primarily because of all the ambient sounds of water, rain, toads, and whales. Walking through those Ages I never felt them to be empty and lifeless, just merely empy of life like people and large animals and bustling towns.