I loved The Expanse and I hoped for more like that. Age of Ash is not it. Extremely well developed world and characters, but a slow paced introduction into a story that is yet to be unveiled. If I had to compare it with something I would compare it with the animated show Arkane, which was amazingly good, but the book lacks the action and the sympathetic characters.
I understand that this is Daniel Abraham's style: slow roasting the reader while he introduces enough of the world and people to initiate explosive events and epic action. However, this means this book is very difficult to rate or, indeed, to like by itself.
The story revolves around two street urchins from the "bad side of town" who get involved into something grandiose that shows what they are truly made of. One of the girls is in full grieving mode after losing her brother, the other is doing everything because of love. Predictably, the positive and negative emotions are influencing the characters in their respective direction.
What I loved about the book is the writing, the depth of the world and of the examination of the characters. It almost didn't need a story. Almost. But it did.
I may read the next books in the series, just to see what happens, but I would not recommend this book as a standalone read. And if you like fast pace, read something else.