Surely it's just a matter of taste.                                 

If you like Dylan - he's a great singer.

If you don't - he's rubbish.

How did Robert Shelton describe his voice in 1961? Something about sounding like a 70 year-old share cropper working in the fields. (Now he sounds more like a 110 year-old sharecropper).

Re those tunes that he "stole" from Woody, Woody "stole" them from somebody else! Hank Williams didn't originate many either.

Dylan has himself said very recently that he is "not a melodist" and that most of his tunes are based on old Protestant hymns.