Suspence, heart, characters you care about, survival
Great apocalyptic world-building. Interesting, believable characters, both men and women.
Nuanced relationships between: Cole (the leader) and Liam (his best friend and co-leader); the older, wiser Cookie and Cole, Liam, the other men, and Hannah; Cole and the men he leads; Hannah and the men.
The group relationships require Cole's and Cookie's work to maintain. They are carefully supported by Liam and Hannah.
Heartbreak, fear, desire, and the addition of Lena and Flynn to the group create complications and suspense. As does the information revealed by the three women about the huge, regimented city called "the Wall." A necessary trade expedition in the extreme cold is successful, but disaster strikes when least expected.
Just like Book 1, Book 2 ends with an abrupt, sucker-punch cliffhanger.