There are probably countless ways to talk about what makes a particular artist compelling, and all of them are true. There are not that many ways to articulate how or why an artist is unique. By virtue of being original, there are few points of comparison and the inability to find a reference point is the whole idea.
American music has blessed us with a great many artists who are both unique and compelling, but it seems safe and not at all reactionary to note they are increasingly difficult to come by. And now, in increasing numbers, they are starting to die. There is nothing we can do about this. It still is at once refreshing and instructive (and, inevitably, depressing) to consider Levon Helm.