Shermer's central message: "People form beliefs before they form explanations for them" is a real game changer, but not an intuitive conclusion. However, this message is well justified by experiment. It has profound implications for how intelligent people can hold opposite (sometimes ridiculous) opinions.
Many great authors have given insight into belief generation and self deception, including Shermer himself. In my opinion this 406 page book now usurps the rest because I find it the most comprehensive and wonderfully compelling account of belief. It is (crucially) grounded in neuroscience experiments - Chapter 6 of 14, for which I admit command of high school biology makes easier reading.
Criticism of "The Believing Brain" would centre around the amount of material openly borrowed from other popular science publications: In this sense, many ideas are less original, but I think completely necessary to achieve a book which properly covers the subject without leaving obvious gaps. Certainly Shermer is well read - he writes competently on everything from theology to cosmology.
People who should buy this book are those who can spare a couple of weeks to read it properly and whose lives have been affected by absurd beliefs which really need concrete explanation. People who should avoid it are those who reject the scientific approach as the unrivalled way of sorting fact from fiction, as they might firmly believe the book to be falsely premised before making up an explanation as to why!