I read this book because I wanted to improve my writing by gaining a better understanding of the formal structure of written English, so I would know what the rules are and when I am breaking them. The author makes the point that breaking the rules unknowingly will alienate some of your readers, undermine your authority in your chosen subject area, and just plain distract and annoy more pedantic types; so you'd better be aware of when you're doing it.
The book does an amicable job of covering the various different types of speech, sentence construction, use of rhythm in writing, avoiding repetition and monotony; and more. I found the sections on the deeper intricacies of phrasing almost sleep-inducing; "almost" being a shame because I was suffering quite bad insomnia at the time, and could have done with something that forcibly made me nod off.
The author makes seemingly arbitrary choices about what is and what isn't "standard written English" without reference to any other authority; but then I'm not sure there really is an official authority on the subject and I guess he's as good an authority as anyone else. At least he can say he's published a book on the subject. In places he points out the folly of attempting to "correct" grammatical innovations in a language which is continually evolving, and notes that slang or other casual constructs have been integrated into standard English over time; in other places he simply states that something is or isn't "standard". I suppose like any author, he is merely stating his opinion, regardless of whether he points this out or not. At times the tone appeared a little elitist; but I'd expect that of someone who chose to write a book describing what is and what isn't correct in terms of grammar and spelling.
I would have liked the book to cover some of the variants in use in English, principally the difference between British and American English. Ideally I'd like to know how to write and spell in a style with allows some sort of compromise between the two; but perhaps this is impossible.
For the most part though, I learned a lot; and there is a lot more in the book that I could have learned too. I should now be able to fluently describe the difference between an adverb and an adjective; if I had only been paying more attention. I wouldn't describe the book as entertaining, but think it would be tremendously difficult to write a book on such a subject that was. If I find one, I'll let you know. In the mean time, Cassell's Guide To Written English does a good job and covers its subject matter thoroughly.