While The Dark Knight forever altered the superhero landscape, the more frivolous Iron Man boasts the genre's most charismatic crusader. Downey's Tony Stark is the waggish yin to Bruce Wayne's brooding yang, and woe to the man who dares trespass on Downey's scenes. His dynamic screen test (among this special edition's four hours of EXTRAS) underscores the hunger behind his pitch to Paltrow: ''Aren't you tired of doing those great little movies that no one sees?'' B+

