xkcd (sic) is an ultra-geeky, minimalist web comic that all the cool kids love. (Especially the Cory Doctorow fan club.) I’m not a regular reader, but I have seen a handful of popular strips that have caught on as memes. Such as this one or that one.
This book is a collection of the author’s favorite strips. Unfortunately, his favorites don’t really overlap with my tastes, so reading the book was largely joyless for me. But I do appreciate what he has accomplished, and I admire his low-art pluck and success. You be you, Randall Munroe, you be you.
If you’re a bigger fan than I, or perhaps just smarter, you’ll probably enjoy it. However, you could just visit the xkcd website and peruse even more strips. Why pay for something that is published free on the Internet? Karma, I suppose, or maybe you want to enjoy the marginalia, which consists of encoded messages, puzzles, and other doodads.