As a slow reader, I've just finished the first 60 pages. As listening to lectures, it's not the knowledge or facts , but the character in mind of the writer, the most valuable part of a book.
I've found some sentences touching me, as listed below
In studying a philosopher, the right attitude is neither reverence nor contempt, but first a kind of hypothetical sympathy, until it is possible to know what it feels like to believe in his theories, and only then a revival of the critical attitude , which should resemble, as far as possible, the state of mind of a person abandoning opinions which he hitherto held. ----------in Chapter 4 Heraclitus
Although Russell didn't succeed according to the statement above when researching on the people too different from himself, like Kierkegaard or Nietzsche, it's still a statement from which I can learn a lot.