To me the "spirit" or the "feel" of the Realms is that it feels like a living, thriving world filled with interesting people (NPCs) who all have their own stories -- whether they be "movers and shakers", humble farmers, greedy merchants, other adventurers, black-hearted villains, The Chosen of Mystra, and so on. It is a setting that has unknown lands and villains, ancient secrets and hidden threats, but also "homely" villages and familiar faces. To me, the Realms are defined by its detailed history, people and lands, that all offer endless possibilities to tell and experience stories. In 4E, most of those people are gone and the world shattered almost beyond recognition. It will take another twenty years to get the same level of detail I have now, so why bother, if it is important to me and my players?