Watership Down is one of my favorite novels. It was one of the first books that I actually read for enjoyment, as opposed to school obligations, and I credit it with helping turn me into the bookworm that I currently am. I can reread the novel again and again and come across some nuance that I missed in my previous readings. In fact, I typically reread it and Dune (another one of my favorites) every year as a kind of summer tradition.
As for the 1978 animated film, I was rather disappointed by the things that they cut out. I feel that the book provides greater insight into the motivations and actions of the characters than the truncated story provided in the film. Overall, however, I feel that the film was a pretty good effort at attempting to translate this amazing story into the visual medium.