David Vernon's Beethoven: The String Quartets is a wonderful book that provides colorful and imaginative descriptions of the music within the context of Beethoven's life and composing career. He has a vivid ability to create almost a screenplay in the mind to describe the music while including some technical detail, most often outlining the various keys Beethoven used. The book is beautifully written with evocative language that makes the music come alive. I found it very useful to listen to the music as I read along.
I only have two quibbles: First, Vernon seems too quick to use pain as a metaphor, particularly for slower passages. To be sure, Beehoven's life was not easy as he dealt with increasing deafness, a variety of health issues, and a tense relationship with his nephew, particularly by the time was composing his late quartets. Doubtless, much of that would filter into the music. But sometimes a piece can be slow and beautiful for its own sake, not as an outlet for personal discomfort.
Second, Venon occasionally veers toward ahistorical comparisons, mostly with the music of Wagner and Mahler (about whom he has also written books). There are moments when he almost seems to suggest that Beethoven was drawing from or gesturing to works by these later composers. Undeniably, they and probably every other composer who came after Beethoven was influenced directly or indirectly by the master, but it seems far-fetched to think that he had any inkling about the music that would come much later.
As I said, though, these are only minor quibbles. I highly recommend this book.
N.B.: Reading Beethoven: The String Quartet has the side effect of causing passages of Beethoven's music to run through the reader's head. This is not a bad thing....