It's hard to know how good an actor Brit Marling is - indeed, whether she's even good at all. In both this one and the other that I've seen her in, the excellent I Origins, she has an opacity to her - a mysterious kind of internal stillness - and I can't tell whether that's a function of the characters she played (it would make sense for the undercover operative infiltrating a radical eco-activist collective that she plays in The East) or rather something that she carries with her into all of her performances. Anyway, it makes her an oddly compelling figure at the centre of this one - compelling in its very lack of expressiveness - and helps to keep the film interesting, together with the inherent tensions relating to whether/when she will be outed and whether each of the titular East's actions against mega-corporations will come off. Also good: Alexander Skarsgard, Ellen Page (of course), Patricia Clarkson.
