'Downton Abbey' Finale Rivals Ken Burns in Ratings February 23, 2012, 11:41 am While the second season of the British import "Downton Abbey" may have drawn some criticism on its native shores, American audiences continue to find themselves entranced by the series. The PBS presentation of the Season 2 finale on Sunday averaged 5.4 million total viewers, according to Nielsen, the highest rating for a PBS program since the premiere of the Ken Burns documentary "The National Parks: America's Best Idea" in September 2009. The second season frequently doubled the average prime-time rating for PBS and, speaking to the strongly favorable word of mouth the show has generated, exceeded the average overnight metered market rating for the first season by 25 percent. Season 3 - which will feature the addition of Shirley MacLaine to the cast as the American mother of Elizabeth McGovern's Countess of Grantham - is being filmed. (Ms. MacLaine is now on the set, and according to Vulture, is "already tweeting Dowager Countess-worthy observations," including the news that "I have Internet but this hotel has no phone service or TV. I feel I am on another planet.") New episodes are scheduled to be broadcast in September in Britain, with the United States premiere to follow early next year.