Interesting plot, likeable characters. Reasonable complexity in the characterizations: protagonists are fallible and villains have some good qualities, but there's enough moral clarity to be satisfying. As an astronomer, I found almost all of the science and technology to be pretty implausible, but that's typical of the genre. The story is riveting and full of conflict, without being as grim as a lot of modern science fiction. Over all, a good read. The narrator is a gifted reader, but she has a tendency to make the characters sound scared or distressed all the time, even when things are going (comparatively) OK.