The one intersection of sidestories and locale that I still remember starkly is the 1.x Falcon Watch or Owl's Nest (I forget which was the one to the East) hamlet's quest lines. The one with the doctor and, separately, with the shepherd, just set an oddly gritty tone that fit so well with the area on the cloudy days I was doing the quests.

After that, the DRK questline. You know which moments.