Heavily relies on the reader having read the novel Watership Down prior.
The first two parts focus on the bunny folk-hero, El-Alhrairah and his adventures. The last part is a story sequence cum novella about events in and around Watership Down after the close of the novel.
If you hankered for more rabbit adventures after the novel, this is the book for you. I liked the folk tales more than the new adventures of Watership Down. As I've no doubt mentioned before, language, history and legend are prime elements of convincing world building and Adams grasped this.