Country vet Merle Haggard isn't the least likely artist to rip through the Great American Songbook. But on Unforgettable, Hag's voice, a tarnished whiskey-soured croon with all manner of rough edges, doesn't lend itself to easy piano-bar interpretations of "As Time Goes By" and "Pennies From Heaven." This is a good thing: Too often we're unable to hear anything in these songs beyond our collective memory of them -- that's the risk that accompanies overfamiliarity with a canon. Yet Haggard gives these tunes a proud sense of experience that has less to do with the sophisticated facility of producer Freddy Powers' smooth country-jazz settings and more to do with the sound of a man flipping through his back pages, at a leisurely pace you couldn't hurry if you tried.