However, if you read about the suit in this post in Slate, you will see the author's victory wasn't because the review was bad; it was because the review was inaccurate. The book was nonfiction, and the reviewer noted that her own name was listed as being interviewed. She claimed she had not in fact been interviewed, and thus cast doubt on the author's veracity and research. It turned out the reviewer had been interviewed, but she had forgotten about it.
So, the answer to today's post subject is: A bad review goes too far when the reviewer states an absolute fact that turns out to be totally untrue. Opinions cannot be proved wrong, but facts can. Reviewers have an obligation to be right if they state something as fact and not merely opinion.
I have to say I agree with the judge. What do you think?