I found this a hard book to read. The writing was excellent. Pierce Brown has improved much since his first book in the series. Like, a lot. His big pro was his storytelling. That has always been good (for me).
It's the same in this book: excellent storytelling. But it was dárk. You can see the implications and problems coming from miles away, from the first chapters in the book. You want to grab Darrow by the neck and shake some sense into him. You watch the horror unfold. Because it's horror, not drama. With horror you know that there will be no real happy ending.
This made it an extremely depressing book to read, and even more so because it's the first in a new series. There won't be any release of the tension until... at least three years on, probably more.

What makes it even more depressing is its accuracy. I often think about those 'ever afters' in stories. What happens after the princess marries her dragon? Or after the revolution has succeeded? The 'we've won, now what'.
In the case of revolutions we see, historically speaking, that you can take the previous government out of the equasion, but you can't take the people from that old world out of it. Same people, same problems.
There's nothing as difficult as trying to rule a diverse people. How would one do it when ones people spans planets? So many old hurts, slights, and so many interests. Pierce captures that extremely well, I think.