I helped edit the first 4 chapters. One benefit of the book is it's short. All the information you need is condensed into 150 pages.
It starts out being immediately applicable (Chapter 2: Write Tests First), giving you systematic methods to measure various happiness qualities. After that, it helps you define what would make your life happier. From there it talks about specific ways to address the types of problems people run into when trying to improve their happiness.
Throughout the whole book, it tries to relate the concepts to programming ideas (testing, specs, debugging, etc). This isn't a general public self-help book, it's specifically for people who program or are technically minded. That's what makes it unique.
If I had to knock the book, I'd say that some of the metaphors are stretched a little bit. Overall the concepts map well, but every so often you're kind of like, "huh... yeah, I guess those are the same things..."