First, I will start by saying that the style of the book takes some getting used to. There is no true dialogue in the book, at least not the kind that most readers will be used to. You will not find a single quotation mark in the whole book. The long unbroken paragraphs and lack of chapters can also be a wall for some readers.
Once you get past these two technicalities, you can start to understand the author's reasoning behind it. The main characters live in a world covered and muted by ash. Thick blankets of it. It permeates, fills, weighs down and swallows every surface and every sound. The writing style that the author uses amplifies this effect.
There are moments of brilliance in the writing. Many lines that could become literary quote-ables. There is also a great deal of over description and repetition that I found myself thumbing through. I know some readers will love the details, but it felt a bit pushed at times and didn't add much to the story.