Blake Shelton may have been an unlikely candidate for superstardom but that's hardly due to a lack of charisma. Shelton possessed a warm, masculine ease that lent his rowdier numbers a sense of sly humor but this relaxed touch also made him an effective crooner of ballads, the ace in the hole that helped him cross over from country to the mainstream in the 2010s. His transition to being a household name certainly was assisted by his starring role as a judge on NBC's hit musical competition The Voice, but by that point Shelton had racked up plenty of number one country hits, be...