COUNTRY'S SAVVIEST STAR ROLLS out another flashy concert special, This Is Garth Brooks, Too!, for NBC on Friday (May 6, 8 p.m. ET). In his shows, the Oklahoma Everyman combines the ingratiating sentimental streak of country performers with the flamboyant showmanship of a rocker. Let's see Def Leppard match the pyrotechnics (literally) of Brooks's "Standing Outside the Fire." Believe me, it isn't easy to be this slick while appearing so sincere. Party on. Garth.