New York Times columnist Brooks dissects, fillets, skewers, then celebrates the American character in his delectable, debatable new book. His central question: ''If middle America is so stupid, vulgar, self-absorbed, and materialistic, which it often is, then how can America itself be so great?'' You may have arguments with his answers, not to mention the question. But Brooks' style is so easygoing and his observations so wicked and astute -- ''There's a rule in the suburbs: The bigger the car, the thinner the woman'' or ''In rural America, churches are everywhere; in suburban America, Thai restaurants are everywhere'' -- that you won't be able to stop reading. Or laughing.