First things first, this is not a book about hedonism or sex. Although the title talks of joy, this is more a attempt to present some interesting behavioural psychology using a quirky framework. So if you're looking for smut or slut, this is not the book for you!
What the book does do is attempt to take the famous "7 deadly sins", and examine them from a psychological point of view rather than a moral one. Many of the sins in question (anger, for example) are not inherently wicked, but simply are emotions that have positive and negative aspects. The author looks to explore some of those more positive aspects, especially those which are interesting.
This is a fairly light read, and I finished the book quickly. The research is presented in a simplistic fashion, but that is good as it helps to avoid getting too bogged down in detail. This is a coffee table book rather than an in-depth study aid, although there are still references and bibliography for further reading if you should wish. After a while you notice that there is a constant phrasing along the lines of: "So they thought it might happen. Did it happen? That's exactly what happened". It can get a little irritating after a while to have these constant affirmative set ups, and I've never come across a writing style that uses it before (for good reason I would now argue!)
My only worry with this book is that it's not especially profound or revelatory. Granted it is intended more as a light read, but I do wonder if I will forget everything in it after a couple of weeks.