To be honest I originally got this book in the hope of finding out more about what happened in the events leading up to The Force Awakens. Bloodline is about bloodlines, more specifically, Leia's and how it affected her in the years following the destruction of the 2nd Death Star.
During the events of Bloodline, we find out that the reforming of the political climate is not as stable as the rebels had hoped it would become. At this point instability in the galaxy is inevitable due to the separation of political factions in the form of the Populists (Leia and other systems who believe that each planet should be in charge of their own laws) and the Centrists (people who believe that the entire galaxy should be led by one central government, like it was during the time of the Empire).
Aside from the central character of Leia, we meet other characters, mainly other Centrist senators and star fighter pilots who currently work for the New Republic. Leia and Han are still getting along very well at this point, just long distance as Leia is focused on being a senator on Hosnian Prime, whilst Han is a captain running flying competitions for pilots (which is a sporting event that is followed by everyone in the galaxy). All we know is that Ben is off travelling with Luke at this point. I was hoping we'd find out more about what Luke and Ben were doing, but that's more likely to be covered in the next movie.
There are hints towards something special about Rey, as there are constant references throughout the book about a major battle having taken place on Jakku. Well it does explain all the old ships that we see in The Force Awakens.
Overall, the story is about how the New Republic falls apart and the beginning of the formation of the Rebellion, along with the fact that The First Order is already in the process of becoming public. The middle climax of the book that pushes some of the action, is a senator working for the First Order and a Centrist "outs" Leia as being the daughter of Darth Vader; which is a secret that is only known by Luke, Leia, and Han.
Bloodline is a very enjoyable read with lots of action and mystery. Other main characters of Joph Seastriker and Greer Sonnel are very well written, you feel like you really would like to go on adventures with them. Ransolm seems a little 'stereotyped' at first, but you soon grow to like him as a character, as well as the fact that he is the one who gives us an insight as to why a nice person might actually support and like the Empire.
Overall a must read for anyone who is a fan of Star Wars and the amazing Princess Leia.