Sometimes simply being refreshing is enough. Take Estelle: she’s a good singer, but not a vocal powerhouse. She’s a fine emcee, but not a magnetic one. And yet, 2008’s Kanye duet “American Boy” was such a shot in the arm; the London vocalist’s flirtatious interplay with Ye was engaging, the hook burrowed deep into the brain, and the splashy electro-funk production sounded  like both a fresh diversion and a remarkably spot-on prediction of the direction pop music would take in […]