Disclaimer: I'm not a very literate guy - or, at least, I'm not as literate as I'd like to be. Such are the wages I pay for not having been more attentive to Mrs. Lundin's 12th grade Lit class in high school. So I don't often get (or identify) the literary tools great authors use to make great, meaningful books. The Narrow Road's... got 'em, however. Days after completing it, I want so to savor the story and all of its layers that I haven't picked up something new to read and there is quite a stack on my bedside table. I just go back and reread some of Flanagan's passages.
Promotional lines co-opted from reviews from various sources and printed on the book cover call this "a masterpiece." I think they may be right. See your local, independent bookseller.