Some of Willie Nelson's best career moves have also been the riskiest. In the early '70s, he became a country star with an image far removed from the music's cowboy past. In the years that followed, Nelson released the classic concept album The Red Headed Stranger and scored an unexpected hit with Stardust, his take on standards from the golden age of American pop. The new Milk Cow Blues finds him exploring the blues through revamped versions of his own songs and covers of both country and blues classics. But with risk invariably comes the possibility of falling short, as Nelson does for much of this unsatisfying collection. His voice is a study in subtlety and suggestion, an instrument not particularly suited to the assembly-line barroom blues favored throughout most of Milk Cow Blues. The voice's inappropriateness, or the inappropriateness of its setting, is only emphasized by the guest stars who join Nelson on almost every track, particularly go-for-broke singers such as Susan Tedeschi and Jonny Lang. Even inspired pairings don't quite work: It's fine to hear Nelson alongside Dr. John and B.B. King, but does the world really need another King rendition of "The Thrill Is Gone"? The pair does better by Nelson's own "Night Life," but Milk Cow Blues' highlight is a solo track featuring Nelson singing alone on "Lonely Street," a quietly melancholy gem that suggests the better blues album that might have been.