I'm ambivalent about this book.
On the one side, it offers a very interesting understanding of how to be happy. The authors defend the idea of an stair of happiness. Each step on this stair is about specific areas of your life. You might be unhappy because of problems you have on each step, and this book makes you reflect about that. Also, the authors believe that sometimes if we have trouble in a particular step of our lives, and we can't make the change we need in that step, perhaps that is because we need to work at a higher step in the stair of happiness. The idea is that the higher you work at making changes in the stair of happiness, the changes you make will trigger down to the steps below.
I find this idea interesting, and I think it may be true. The book also helps you identify what sort of thing is making you unhappy, and therefore what sort of thing you need to work out. That is, it helps you identify in which step of the stair of happiness you need to work at. However, it doesn't help you figure out what changes you need to make for you to be happy. Therefore, this makes the book a bit impractical.
Of course, you cannot expect the authors of this book to come up with solutions that will work out for every individual reader - we are all so different...
I'm just saying that one may have to work very hard at figuring out how to improve one's life and be happier. The book comes with an approach that might be helpful, but not with solutions that will work out for everyone. A lot of self-reflection is needed.
So this is why I give this 3 stars. The book might be a very good starting point, but further work will be needed.