Lodovico spotted a user review from Martin over on the IMDB boards, which has some nice things to say about Natalie’s performance. A performance that another poster thinks is going to be pushed as a supporting performance by the studio, even though its technically a lead.
I saw this film last night, and the acting is superb all around. Natalie Portman shows the ability I saw in her as a teen but which has been mostly dormant in her adult starring roles (her supporting turns have always been fantastic though). The actor who steals the movie, however, is 10 year old Bailee Madison. She is the heart of the film, as we see how all of the conflict (not just familial but the greater conflict between our nations) gets concentrated in her tortured soul. This does not appear to be a performance that was assembled in the editing room. She appears to be fully in control, and she is the heart of the film. Her performance will haunt you. It is perhaps the best performance I have ever seen from an actor under 12.