Ah, Willie. One of my very favourites. His phrasing is definately his own, and his guitar playing is unique. I think he is one of the greatest songwriters of our time. And I agree with Moonchild, you haven't heard a Willie song sung until you've heard him do it (with absolutely no disrepect to Patsy Cline, Faron Young, Ray Price etc), although Aretha does and awesome job with Nightlife.
Willie plays and sings by feel. And I think more than anything feel is what music is all about. His timing changes with his mood, so each song is fresh.
The other thing is, you haven't heard Willie until you've seen him live. His shows are absolutely spellbinding.