The quibbles first.
The book, at over 500 pages, is too long and runs out of steam in the final chapters.
The style, while engaging and accessible, can sometimes become indulgent and over folksy. Sentences like "it's my book, so I can write what I want" grate.
Her minute dissection of the intricacies of the English class system are extremely funny, precisely observed but become exhausting after a while.
However, as a voyage through the essentials of Englishness, this is a tour de force which I would challenge any English person to read without experiencing many moments of disarming self-awareness. Kate Fox does not sugar the pill in her presentation of the repressed and emotionally constipated race that we have become. Some of her set pieces (how we say goodbye at the end of dinner parties, pub etiquette, our obsession with gardens, etc) are wonderful and illuminating. How the book reads to foreigners would be difficult to judge - I imagine those closely familiar with England would find it chimes loudly, while those who are not would probably not believe how strange we are. To an English person, however, this is as close to a definitive guide to the emotional make-up of the English mentality in the 21st century as you are likely to find and, as such, despite a few reservations, a triumph.