Totally Biased -- I think the early Dylan voice, up till about John Wesley Harding, was an amazing instrument, with a few notes (like a drone, perhaps). After that it got whiny, and less expressive. He seemed to hit more notes and did less with his voice. It is a voice you have to develop a taste for. I kept trying to hate it, and got over that.
Woody Guthrie never had a great voice: Leonard Cohen was blessed with a leaden voice -- There is hope for all of us.
yours, Peter T.