One-third amazing, one-third good, and one-third awful, Bubba Sparxxx’s third CD, The Charm, is a frustrating missed opportunity. The white rapper is insanely talented — his drawling flow stays loose and casual even as he’s spitting taut verses. And when content and groove dovetail on the blue-collar lament ”Ain’t Life Grand,” he’s an A-grade artist. But tired crunk tracks like ”Ms. New Booty” keep the self-proclaimed country boy from getting his blue ribbon.