I had a discussion with my 16-year-old son yesterday about how to review a book. One thing I pointed out to him is that it is easy to trash a book if you didn’t like it, but it’s much harder to ask what you didn’t like about it and whether that problem is with you or the book. If the former, then it is the responsibility of the reviewer to look beyond his own prejudices and tastes and try to assess the book on its own merits. If the latter, then the reviewer should note what the specific problems are and provide helpful feedback to the author via the review.
I’ve read too many reviews on the Web where the reviewer acts as if the book were not worthy to use as toilet paper. That sort of review is not really helpful to anyone. Instead, it acts as a censor: “I didn’t like this book, and I’m sure going to make sure you won’t either.” A much better method is to lay out what you found problematic and let your intelligent readers decide for themselves.