There's no one else I can think of that has the compelling voice of Alyn James. I once heard someone say about Louis Armstrong: "Great ideas, perfect pitch. The voice - got a problem with that? - you wish you could sing like Louis." It's that one-of-a-kind voice that I'm talking about.
I've always felt that, regardless of the instrument or voice, if you can identify him/her within 5 notes, they've reached the top: originality, uniqueness. 'Nuf said.