Book review is a popular tag because of the number of blogs that review books and the rise of so-called litblogs ("literary blogs").
A book review is an analysis of or commentary on a particular book or books or even a series of books. Book bloggers may review all genres or just specific ones, such as romance, science fiction or even graphic novels.
The popularity of book review also reflects changing times. The book review was long the almost exclusive province of weekly, biweekly or other periodic print publications. As book blogs increased, debate began about the value of book bloggers. Now, however, some standalone print book review sections are being downsized or shut down. The blogosphere may be the future for the book review.