Ian McEwan's short novel is an interesting excercise in point of view. It is the story of an estranged couple seen through the eyes of their son-in-law. It's a unique approach that gives the story some distance, but I wonder if it is too distant. I don't think this is his best novel, but he does what he does best as a novelist, which is make us think about the darker side of humanity.
Another thought: Black Dogs is very much a Twentieth Century novel, so in some ways it is outdated; but in others the themes ring very true in relation to the issues of today.