Overall: VERY GOOD. I flew through this. At times it bogs down slightly in the super intricate politics of Europe in the 1930s, mostly towards the end, but overall, really fun, super engaging. He's awesome at pulling in these tiny little threads of magic realism that add a little flavor without being distracting or out of place.
My only gripe was the last chapter, which was pretty disappointing. I was a little worried about the women in this book, thinking "He's writing cool women, but where is this going." and wondering if we were going to have a Magical Unattainable Unknowable Woman Problem. And I thought, Well, maybe not! But then it turns out we do. So, in terms of his entire canon and how he writes women, it's a little closer to Veronica in that respect. Which is fine, just not my favorite.
In general I would order his books from least to most favorite like this:
* Franklin Flyer
* A Trip To The Stars
* The Bestiary