THE Gate Theatre certainly seems to have found the recipe or wowing the American critics. First there was the unstinting, if ungrammatical, appreciation of the theatre's Beckett Festival. Now Donal McCann has become the object of adoration for his role in Sebastian Barry's The Steward of Christendom. "A world class star has come into American theatrescopes," says a page long paean to McCann in Newsweek, which also quotes a star struck spectator who inquired "Who is this guy?... He's got to be the world's greatest actor." And how exactly did McCann, get to be so insanely great? As far as the piece's author, Jack Kroll, is concerned, it helps that McCann.... has an ego about one twentieth the size of a Hollywood bit player.