Mira Nair (Monsoon Wedding) directed this adaptation of William Makepeace Thackeray’s best-known novel. It’s no Barry Lyndon (Stanley Kubrick’s 1975 take on Thackeray), but the first half is better than average for an opulent Classics Illustrated film, thanks to realistic period detail, brisk storytelling, and Reese Witherspoon as the saucy rags-to-riches antiheroine Becky Sharp. Then the whole lumbering weight of the production catches up with the filmmakers, slowing the proceedings to an interminable crawl. With Jonathan Rhys-Meyers, Romola Garai, Gabriel Byrne, and Bob Hoskins; written by Matthew Faulk, Mark Skeet, and Julian Fellowes. PG-13, 137 min. (JR)