3.5 stars. I would say "I liked it," not "I really liked it." These guys are pretty smart, and their points are well argued & developed. I don't really know if it lived up to its title much, it didn't really deal with IMPROVING health much, and it didn't mention happiness much at all (although I guess for a lot of people that would be tied to improving wealth, which the book does deal with extensively). When I first started this book there were a couple things that bothered me (like the way they used the word "prove" in a scientific context when obviously that was not the case, or how they referenced Blink--shudder. Could they really not find the original study? And if they couldn't, why bother using the info at all?). However after reading the whole thing, it got better after the intro and I did put several sticky notes in it to mark some especially interesting information.