Watership Down was a fabulous book - and though panned and forgotten by critics, Shardik was a powerful memorable book as well. 

Perhaps, since Watership Down does have a 'message' that fixes it too strongly in a particular place and time,  it will not be the timeless classic that Winnie the Pooh or Wind in the Willows have become.   But wonderful to read all the same, and not just for children.  Quite puts the simplistic narrative of a J.K. Rowlings to shame.