Book reviews may be the only source of analysis for very recent books, and sometimes for children's books. However, book reviews generally do not have the same depth that an article of criticism has.
Warning! Most instructors will not accept reviews posted by users at sites such as Amazon or Barnes & Noble.
Web-based magazines and blogs sometimes include substantive reviews. Consider, for example, the Slate Book Review.
These two general-purpose databases cover a wide variety of popular magazines, book review sources, and scholarly journals.