In BiblioCommons, there are summaries and reviews (if any) within the item record details. You can find “Opinions” towards the bottom of the page from the Critics (official reviews) and from the Community (other library users).
In the Classic Catalog, perform your search and go to the detail page for the item you are interested in. Look for the “Reviews & More” button near the bottom of the page. Clicking this provides any available reviews, summaries, and additional content information.