As a narrative, it's a bit weak. But on other levels, this film is fascinating. The cast, especially Sarah Polley, does a bang up job. Every character real and believable - even the kids.
First and foremost, the film is a strong advocate for "viva la vida" (Frida Kahlo before Cold Play!). There is an old Buddhist parable about a man running from a tiger and suddenly faced with a cliff. In one direction, the tiger; in the other, the cliff. He looks down and sees a branch growing out of the rock. Somehow, he casts himself down and grabs that branch. The tiger looks over the edge at him. He doesn't think either he or the branch can hold on too long. Then he spies a wild strawberry near the branch. He grabs it and eats it. It is the very best strawberry he ever ate in his soon-to-be-over life. And so it is with our protagonist. Having the harshness of mortality shoved in her face at a young age, she begins to live each day with full attention. Something humans hardly ever practice.
Second, the interesting, but perhaps unrealistic, decision to withhold her diagnosis and prognosis from everyone, creates an entirely unexpected space. She takes her cue from Dr. Thompson (Julian Richings), who can't look someone in the eye and tell them they're going to die. From there, she decides not to put anyone else in Dr. Thompson's situation. This frees us from the overly maudlin watching someone die thread.