The subject being spoken of is without fault. The phrase dates from the second half of the 1900s and was extremely well known by the 1970s. In a cartoon strip “Juliet Jones” in the Lowell Sun of August 1974, a woman describes a man, saying, “He’s brave, handsome, industrious, an enemy of criminals. . . . what’s not to like about such a man?” Occasionally the expression is used ironically, applied to something the speaker considers quite unlikeable. Thus a Newsweek article opposing health-care reform was headlined “What’s Not to Like? Reform? Why Do We Need Health-Care Reform? Everything Is Just Fine the Way It Is” (July 31, 2009).