I didn't realize how good a singer he was until I heard him sing something (I don't remember what) last Thanksgiving that I hadn't heard him sing before. He was fantastic.
I also like his songwriting (or at least his choice in music). I'm not a country fan, but there are certain country artists I like anyway, and Willie Nelson is one of them. His music sounds very genuine to me; not country trying to be rock. Garth Brooks I also like.