especially a nonfiction book

I'd argue this is at least as relevant for fiction books. Most books that are considered "good" or "masterpieces" haven't earned that from the story but from how it is told, from the language used, the writing style, how a greater picture is painted. Any German student who had to go through the pains of reading a Thomas Mann novel will know what I am talking about, that dude could have written a 150 page book with 90 sentences. Of course you can read an analysis of symbolism and style characteristics used and the plot summary, but it isn't the same as reading the novel, as the story will not grasp you in the same way. It's not about the content, it's about its presentation. (In the case of Thomas Mann the pain is a vital part of the presentation.)