The plot seems to carry itself around the idea of the world ending and it's tragedies. There isn't a linear plot and that's not a bad thing necessarily but it can make certain parts of the book a slog to get through. Although you see the characters evolve the point of view of the story can be limited - many times it's an observation of how people react rather than insights on how they or the protagonist feel. When I was invested it was really good, when I wasn't I was waiting for the next major plot point.