This top-of-the-line country ballad is nothing new except for the fact it's by the woman behind the best-selling song of this century. Long one of the great cross-genre pollinators, Shakira's excellent Blake Shelton duet shows pop-country the same care and melodic justice she did Afropop and hard rock, adding another tune to the classic canon of love-over-whiskey songs. Only in American pop is she still underrated, which puts her in good company with the metric system. D.W.