Like Gideon, this book took a significant amount of time for me to go from "what the hell is going on and why does it matter?" to "what the hell is going on and I need to know more!"
More, actually, which was frustrating. It felt like a mismatch between the writer's expectations and my own - I had a good sense of what had probably happened and I just wanted to get to that part rather than deal with all the preliminary confusion. 
Also, I missed Gideon's voice from the first book. A significant amount of that book's draw for me was that Gideon was delightful. Harrow, especially for the first two thirds of the book, is just a lot less fun to listen to.
Having said that, there were some absolutely stellar set pieces and lines in it and the last third of the book was what I had come here for in the first place.
But it was still, at the end of the day, way too much lead-up relative to payoff.