I am a big fan of ‘Firefly’ series and ‘Serenity’ movie as well. But this particular novel is mostly just a novelization of the ‘Serenity’ movie. Yes, it definitely gives you more inner emotions and thoughts of characters than a movie can do. But still it is just a text version of the story you know (if you watched the movie), slightly adopted screenplay, I guess.
The novel is good for fans, and I even want to re-watch the original series after that, but really don’t expect a lot here.