I think Mr. Barrett makes some good points but I still found this book hugely interesting and would even go so far as to say it should be required reading for any politician, salesperson or marketing executive. Why? Let me explain.
Here, as I have not seen elsewhere, you have a multitude of evidence, based on a review of psychological studies, that suggest numerous conclusions about how people think, feel, and act at the most elemental level. It is true that we are never presented with any controversial results (polemic about tests referred to, tests which would show contradictory results) so we act on a faith in this man's erudition, research, and knowledge that what we are being told is the conclusion of an exhaustive study by a top practitioner in the field. In my opinion, this is a hugely exaggerated assumption but, assuming it is correct, then the books quoted research studies and their conclusions are massively important and should be studied by the professions mentioned above and by intelligent people everywhere.
More well read readers might indicate that there are other sources of such information that are more convincing or better presented. I have no such reference, so I can only state as a second reason to read this book that the material for me was original: I had never seen reference to as many studies and the arguments are logical and convincing. Also the simple clarity presented by his research examples and conclusions leaves one with little doubt that he is an authority and therefore that this material is important.
I do not think drawing more conclusion or a world wide theory was the aim of the book. It is an assemblage of conclusions which show tendencies, if not very strong tendencies. Note that he always refers to examples where a majority of respondents choose a particular outcome or sentiment (it is never everyone that does so).
I have read this book as someone interested in Vipassana meditation and the lessons it teaches on approaching life equanimously: that is with calm and serenity, avoiding to judge, avoiding to generate negativity and focusing only on an observation of reality as it manifest itself. In this book, the author is questioning how we perceive reality, not so much in what we observe but in how we interpret it and therefore in how it manifests itself as perception. Vipassana does offer to those of who want a more holistic theory an answer that this author does not necessarily give: that is to avoid the distortions of the mind and the feelings one must observe without feeling and without value judgements.
I would heartily recommend this book which also reads well and is humorous to boot.