Florin Scanlon’s review published on Letterboxd:
From the writing-directing duo Brit Marling (who also stars in the lead role) and Zal Batmanglij that brought us Sound of My Voice comes this thriller about an agent who works for a secret intelligence firm infiltrating an eco-terrorist organization. Like with their previous movie, most of the time is spent inside this group/cult, with a newcomer (the audience's vessel) learning why the members are doing what they're doing and coming to understand, even if partially, their reasons and beliefs, maybe changing the newcomer's perspective or at least providing a different angle to a subject. Sound of My Voice suffered greatly from a lack of believability, or better yet, an unsatisfying approach to the subject at hand, trying to be very serious about what it tries to say but failing to support that due to the borderline ridiculousness of the characters' actions, behaviors and the almost annoying (or laughable, depending on your mood) way these are shown. The East is guilty of this as well but with a slightly more believable story, better cast, better written characters and more thrilling moments it avoids being as clumsy as its "spiritual" predecessor. The manner in which the plot advances is still unconvincing and there's that ever-present air of self-importance that seems specific to the aforementioned creative duo but all in all it's quite a decent thriller that manages to make you question things, even if only for a quick second.