For me it's been the 'folk' aspect of the music: this is music that might be composed by anyone with something to say, a story to tell, an emotion to express. These are songs anyone who can carry a tune can learn to sing, with or without accompaniment. They can be sung plain and simple, or decorated to the extent of the singer's ability and creativity.

Like Don Firth says, this music has roots: the brand-newest, just written yesterday folk song rests on the knowledge of how and why such songs have been written before. There is a continuity of human behaviour, human emotion, human events, recorded in folk songs, from the four hundred year old ballad to the newest crafted story-song.

Besides that, most of it sounds pretty good as well. ;-)