Criticisms v. Reviews
Literature, or literary, criticisms are works that provide an analysis and interpretation of a literary work. Those writing criticisms may look in-depth at themes, plot lines, and characters within the work. Authors of criticisms may also apply specific theories to a work which allows them to present and critque the work through the a particular lense. For more information see: Purdue OWL
Book reviews, on the other hand, may tend to focus more on the merits of the work, how well (or not) a work is written, or its commercial success. Some reviews (for example, The New York Times and Los Angeles Times Book Reviews) may be fairly long and provide some analysis. While these can be useful for your research, it is best to begin with searching for criticisms published in academic journals.