I'll start. I like it when players stop to watch world events like the Jester Festival shows, it makes it feel like players are an actual part of the world.
I enjoy stumbling upon small overland scenes. You're running around these large zones, and then you come across a river which has a skeleton with an arrow in its back and a backpack nearby. Or when you come across a small hunter's hut in the wilderness that has game hanging. It's the smaller details like that which make the larger zone feel even more alive.