Like many other reviewers, I bought this book after watching AMC's adaptation for TV. The sound quality of dialogue on the show was terrible and I felt like I was missing key parts of the story, so I bought the book to fill out what I was missing.
I am glad I did!! The show was (as adapted shows or movie versions often are) a pale shadow of the book. I was impressed by the amount of time Dan spent researching this expedition, its members, archeological expeditions to locate the ships and crew, Eskimo culture and language, and how polar expeditionary ships were reinforced and otherwise outfitted. Like Erik Larson's "Devil In The White City" and "Dead Wake", this book brought historical events alive and inspired me to seek out more information about the events described. It was a fascinating, well-paced read, and put me in the era through the effective use of dialogue. I looked forward to reading another chapter of this book every night or more on weekends. I love it when a book does that.
The story adds some fictional elements that historical records could never be the source of, but these are added to produce a very compelling story explaining the disappearance of two ships' entire crews (minus the 4 bodies found in graves on Beechey Island) beyond merely explaining that "poisoned food and exposure got them all".
The TV series made some significant changes to many of the events in the book, and I can guess that some changes were necessary for a shorter miniseries, but others seem to have been made for convenience. For example (MINOR spoiler), in the TV version, the Eskimo girl Silna is initially silent after the death of her father, but then is seen helping Dr Goodsir add to knowledge of Eskimo vocabulary by teaching him a few words. Later, she cuts out her own tongue for reasons we don't know. In the book, Silna is silent from the beginning. We learn much later that she is part of a small group of "sixam inua" (Spirit Governors) who communicate with the Tuunbaq telepathically, and who have made a pact to both communicate with and offer food to the Tuunbag. This pact is sealed when the sixam inua offers his or her tongue to the Tuunbaq, who chews them off as a sign of acceptance. I'm not sure why the TV series couldn't have shown Silna out away from the ship somewhere making this offering. My guess is that doing so would have let viewers know that Silna had some kind of control of the spirit/monster/beast.
The TV series had an odd ending that was disquieting and VERY different from the book's ending, which was rather a happy one, considering that this is a book about ~300 people either murdered, dead of disease (scurvy is nasty!), exposure or starvation in the Arctic circle. The TV series should act as an appetizer for the book, and once read, you will feel much more satisfied in having lived a good and complete story.