I depend almost entirely on reviews for discovering books that sound interesting and enjoyable to read. The best reviews, I think, provide a balance between a factual description of the book and the personal opinions of the reviewer. They usually include a summary of the content, though in the case of a novel it is infuriating when they reveal too much of the plot. There is also a discussion of the context, perhaps citing similar books and filling in the historical or cultural background, acknowledgement of the book’s good points and constructive criticism of its flaws. Writing a review, as I was sometimes asked to do during my former academic career, is quite an art. It takes a lot of time to read through the book and take notes, perhaps do some research about its subject-matter, and then compose a piece that is fair to the author and will hopefully prove interesting and informative for potential readers.
The detailed reviews in quality publications such the Listener, Spectator and Literary Review are often worth reading as essays in their own right, even when the books in question do not appeal. Many of the shorter reviews on public platforms such as Amazon and Goodreads are also well written and thought out, but a few of them represent individual opinions of an extreme kind, ranging from lavish praise to abusive condemnation. Some of the good ones have been paid for by the authors; some of the bad ones say more about the prejudices of the reviewer than about the book itself.
Many books never get reviewed at all, so from the authors’ perspective perhaps any review is better than none for publicity purposes. However, all but the most stoical authors feel a certain trepidation before looking at their reviews. Some have been so badly angered or upset by reading them that they no longer do so. While most of my own books have received positive reviews, and these are highly gratifying, it is the occasional negative one that can stick in the mind and feel soul-destroying. And it is baffling when there are completely different verdicts on the same book. Having recently been devastated by a 1-star rating of my Three Novellas on one site, I was comforted to find on its Amazon UK page a 5-star rating with the comment “Jennifer brings together all her experiences from previous work to produce a superb trilogy finishing with an interesting twist.”
I would encourage reviewers to be kind as well as honest, remembering that all books have both good and bad points, and that those they hate might be loved by someone else and vice versa. Personally I no longer post ratings or write reviews for books I dislike, but prefer to give up reading them and move on to something else.