Writing a good book review is not an easy job. I've been writing book reviews regularly, for some years now. I am also a big consumer of book reviews. I suspect it is so because I am very grateful to this particular literary genre: my interest in classical liberalism was awakened by a book review, namely the review of the Italian translation of David Friedman's "The Machinery of Freedom". The author happened to be Sergio Ricossa, an outstanding economist and a brave fighter for economic liberty in Italy back when Keynesians were the right-wing of academia. Though I read it some 17 years ago, I do still remember the article: it was delightfully witty, as the book itself is.
The book reviewer has a substantial responsibility: her piece will be, more often than not, the only contact the reader has with a particular book. You need both to present an author's arguments fairly, and to make your case on why a book is relevant - or is not. Sometimes book reviews degenerate into opinion pieces, as the writer takes a book as a convenient excuse to make her cause for or against a particular policy / set of ideas / scholar. These are typically bad book reviews. But bad book reviews are also those in which the reviewers aim to present all the major arguments advanced by the reviewed author. This is a daunting and almost impossible task, if the book has any substance. The reviewer needs to provide her reader with a glimpse, the scent of the arguments; she needs not explain or demolish all the author's points; she needs to do a good service to the reader, providing some basic information on the reviewed book (whom was it written for? is the language accessible? should it be read cover to cover or can it be consulted from time to time? what kind of debates is it engaged with?) but also offering a sense of the style, tone, and argument of the book. You should not finish a book review thinking that you agree or you don't agree with the author's thesis. You should finish a book review having realized whether you do or don't want to get engaged with the author's thesis, i.e. to read the reviewed book.
Sometimes you stumble upon outstanding pieces (as you know, for example David Henderson is a fantastic book reviewer). An example is this book review of George H. Smith's "The System of Liberty" written by Henry Clark for the Library of Law and Liberty. Smith's book is a remarkable contribution to the history of classical liberal ideas. Clark does a very good job in presenting Smith's arguments and central thesis, and strikes the right chords. By reading it, you'll get a good sense of what Smith's book is about, and you'll recognise if it is a book you may be interested in reading, either because you agree or because you believe it's worth disagreeing with it, or if simply its arguments do not matter to you at all.
Everybody has books that consider important and cherished. But do some of you remember the reviews that allowed you to get to know these very works? Everybody has favourite books - but do you have a favourite book review too?