We give our opinions on a frequent basis, and if you think about it, you might discover your opinion is based on a criterion, whether that criterion is your personal taste, a theoretical model, what you know about right and wrong, or even a fact or two. In college you will be asked to provide your opinion in a more formal way. We call these tasks, and sometimes full assignments, critiques.
Writing critiques improves your critical and analytical thinking and hones your evaluative skills. While a summary is meant to represent the original source faithfully, a critique is meant to be a critical assessment of the reading material.