A new Imax film about the devastation wreaked by Hurricane Katrina seems a bit incomplete, as it somehow manages not to say a word about the political and societal dysfunction that have made Katrina a lasting blot on the American landscape. So “why does a film that seems so insistent on decrying the loss of wetlands end with little more than an anodyne lament and some empty hope? Roll the credits: The film was made with money contributed by Chevron. And Dow Chemical. And Dominion Exploration and Production, a major power company.”