This is truly a marvelous piece of work. I can't imagine the amount of time and research that went into crafting this epic - and that is truly what it is. The author takes so many different perspectives - historical, psychological, biological, evolutionary, etc. to explain the decline of violence over the course of human history, and it is truly amazing and engrossing to read.
However, I had to dock a star for a few reasons. First, I believe Pinker uses excessively obsolete and/or "advanced" vocabulary throughout the entirety of the book. The vast majority of people reading this book, I believe, will have a very difficult time reading the book without a dictionary nearby (or of course, an app on your smartphone, which I admittedly used). I have a college background in writing, and was proficient in writing throughout my schooling days, but Pinker's vocabulary is advanced to the point of being frustrating and annoying; I found hundreds of words throughout the ~ 700 pages that I hadn't a clue as to their meaning. Eventually, it became frustrating enough that I downloaded the Merriam-Webster dictionary app for the sole purpose of having it on hand while reading this book! Never had that problem with any other book.
Second, Pinker tends to run off on tangents on a consistent basis, and you will often forget you are even reading a book on violence. Many of these tangents are relatively interesting, but at times I thought perhaps he was just stroking his own ego rather than staying on topic. The book could have been much more concise and delivered the same message.
As a whole, however, the book is excellent and definitely worth a read, if you are up for a challenge. Or hey, maybe I'm not as great a reader as I thought I was! I found it a challenging but rewarding read and I came away from the experience with a great deal of knowledge and insight.