Nonfiction is such a huge category. In my mind, I tend to divide it between works that are trying to describe things and works that are trying to make some normative point about the world (there are also personal narratives, like memoirs). Obviously, there is alot of overlap here, because most descriptive books also contain some element of "This is how things ought to be." And either of those things can contain enough of a personal narrative that they might qualify as memoirs. In a rough sense, the division is between polemics and history books.
Although they contain many facts, I'd say that The Feminist Mystique, Studs Terkel's Working, Silent Spring, Arlie Hochschild's The Second Shift, Marcus Aurelius' Meditations, Allan Bloom's The Closing of the American Mind, and Tolstoy's What is Art? all fall into what I'd call the polemical mode.
In general, I tend to respond better to polemics (even when I disagree with the essential point) because there's something very charismatic about listening to a person who believes so strongly in what they're saying. A good polemic provides a measure of security in this world: it tells you that values and standards do exist and that it is possible to arrive by them through some mix of belief and reason and intuition.
However, I have also consumed a number of more straight-forward explications in my life. Amongst these, I tend not to prefer books that are straightforwardly about personalities or mere recitations of events. I think that once upon a time, especially in the 19th and early 20th centuries, there was a fashion for books that were about events and people. And I just can't take those. Any biography, in particular, that doesn't aspire to be more than just a description of a person's life, is boring to me.
I need a book that attempts to use facts to systematize and try to understand the world. That's why my favorite biography is Robert Caro's The Life of Lyndon Johnson. It's an amazing, sprawling set of books (I've written about before), that's about nothing less than how government works, on a practical level, in America. By looking at Lyndon (who was an awful man, though a fairly good President) and the people that he encountered and befriended and destroyed and the institutions that he changed, the book shows us how the sausage gets made: How does someone get elected? How do they maintain power? How do they create and pass legislation?
It's hard to tell when a book is going to be worthwhile in that manner, because many people just read nonfiction books because they like colorful stories. Thus, it's possible for a nonfiction book to receive tremendous acclaim even though it doesn't really have much analysis. Randy Shilt's And The Band Played On is a nonfiction book with almost zero analysis, for instance. It doesn't look at why the public didn't respond to the AIDS crisis or why men's organizing efforts failed or didn't fail in the way they did. (I'm not saying that was a flaw in that particular book, since that wasn't its mandate. The book was written in the midst of the crisis and its role was simply to capture the facts. I'm just using it as an example).
This is a really long way of saying that I am in love with Richard Rhodes' The Making of the Atomic Bomb. For the first twentieth of it or so, I was engaged but mildly dubious. It seemed to be spending lots of time on the personality and life history of various physicists and on the details of physics experiments that I only sort of understand. But then it went into a long riff about World War I and poison gas and the mechanization of warfare (as a prelude to the line of thinking that would make the atomic bomb seem like a good idea), and I was completely hooked. Last night, at 1 AM, I was like, "Hmm...I could just stay up for a few hours and read this..."
Now the book is about Budapest and how Hungary created a lot of stellar atomic scientists! Not sure how this will fit into the larger storyline, but I am loving the section! (I do have a weakness for the Austro-Hungarian empire. Everything I've ever read about it makes it seem simultaneously schlerotic and vibrant. And it produced some amazing writers: Joseph Roth, Robert Musil, Stefan Zweig, Dezső Kosztolányi)