From a craft perspective, it's amazing what Donoghue accomplished--telling a story that adults might find spellbinding from the point of view of a five-year-old. She took such extraordinary risks--she didn't change the setting or the tone much at all, the reader began to the monotony of their schedule and feel trapped in the room, too. Pacing was fantastic. And yes, you can tell a story with little or no backstory for the first 100 pages.
From a storytelling perspective, she did a masterly job. It contained some of the most intensely suspenseful scenes I can remember reading of late--my own heart was pounding. This book made my feel physically sick because the story was told with such power and detachment at the same time.
I actually gave it 4.75 stars just because I got a little tired of Jack's voice and mentions of poo at every turn during the last third of the book. The last third of the book--after they are rescued--was disappointing. Why the protagonist chose to give up at that point following a valiant struggle lasting years just didn't seem realistic to this reader.
Riveting read. If you have a weak stomach for stories recounting human perversion and tragedy inflicted on others by others, this is not the story for you.