It’s no mere coincidence that pianist/singer Norah Jones, who’s paired her sublime vocals with Willie Nelson’s on a few Grammy-nominated duets, calls her sporadic side project The Little Willies, as the band’s follow-up to its 2006 debut is a second session of the eclectic, genre-shifting kind that Mr. Nelson has made his stock in trade.

While the spirit is similarly loose and the musicianship grand (particularly the old-style country licks of guitarist Jim Campilongo), the album’s overall emotional weight is a bit slight, owing to its semi-novelty feel. But even if the whole affair is something of a lark, Norah’s songbird stylings and The Willies’ uncluttered arrangements send it skyward, as do such standout tracks as an enlivened, Louisiana-spiced version of Loretta Lynn’s “Fist City” and a cover of “Lovesick Blues” slowed to a lusciously languid crawl.

Is it country? Jazz? Hillbilly lounge music? If such matters hang you up, you better move along—the band’s willy-nilly but affectionate, bohemian approach all but renders those questions irrelevant. Even now, Willie is probably smiling.