Roy Lichtenstein's popular appeal--and his influence on pop culture, seen in everything from greeting cards to sitcoms--at times overshadows his importance to contemporary art. Yet, examined on its own terms, Lichtenstein's comics-inspired, deadpan artwork remains as truly unsettling to art-world orthodoxies today as when it first gained wide attention in the early 1960s. Lichtenstein (1923-1997), a central figure in Pop, consistently savaged the rules of painting--while remaining committed to the most traditional procedures and goals of the medium. (He once said, "The things that I have...