If you don't have plans to see this movie, you can check the spoilers here and then come back.
Enthralling, engrossing and frankly terrifying at times with a last half hour that will blow your mind, this is maybe the most intense and well-done psychological thrillers I've ever seen and among the better flat out movies I've been to in quite some time. If ever I've seen an instance where a director can be a star, it's here, as this film has Darren Aronofsky's fingerprints on every aspect and is the better for it by far. It's got all his signature flourishes from the surreality created by the way he shoots to the excruciating focus on the physical pain a body can endure to the slow descent into paranoia that makes the last act incredible; you can see the love and care bordering on obsession this filmmaker had for his subject matter. However, as much as Aronofsky brings as a director, Natalie Portman matches him as an actor, delivering the most breathtaking performance I've ever seen her give. Her metamorphosis over 108 minutes is measured and powerful, mirroring the transition of her character from model of tortured restraint to out-of-control dynamo perfectly. Her line readings are great, but what really sells it is how much she gives of herself physically, from her face to her movement; you can feel her struggle and get swept up in her pain and (here's that word again) obsession. The rest of the cast is dynamite as well, in particular Barbara Hershey walking the line as Portman's Nina's caring but somehow unhinged mother; she does a great job keeping you guessing as to what's really in her head, has amazing chemistry with Portman, and can jump from maternal to chilling on a dime. Vincent Cassel provides solid glue as the visionary but philandering director while Winona Ryder has little to do but is well-cast as a dancer just past her prime; the worst I can say about Mila Kunis is I felt she wasn't quite on Portman's level, but that's a near-impossible thing to ask here and she did solid work. This is also that rare movie where I really noticed the sound work, from the way passing subway cars sounded like ruffled feathers to the rising and falling volume of Portman's breath. And while I'm at it, let me praise Mark Heyman, Andres Heinz and John McLaughlin for a brilliantly-written story and script as well. Just an incredible movie all around and one of those times I can't really do it justice with words, so just go see it!