The film is in a better state of mind than its characters. Its humor comes, as the best humor does, from an acute observation of human nature. We have known people something like this. We smile in recognition.
Kidman, doing her best work in years, just comes at you. Her final scene with the splendid Wiest, who builds her character with uncommon feeling, is devastating. So is the movie. It takes a piece out of you.
Rabbit Hole is a tremendously sad movie, but it's also the furthest thing from a miserablist wallow, portraying grief as something that doesn't arrive in neat stages, but in unpredictable waves with forceful undercurrents.