Personally, I try to avoid using the term "negative review." But Eric at Pimp My Novel doesn't mind using it. He did a post last month called On the Importance of Negative Reviews.
Among the things he has to say:
"...one of the principle reasons why, à mon avis, the negative review should be written: to help correct the bias generated by solely positive reviews, since such reviews are oftentimes met only with silence by those with dissenting opinions."
"...rarely do we question a positive or even neutral response to a book, but as soon as someone indicates that they didn't like—or even flat-out hated—that book, we immediately want to know why."
I would go even further and say, Rarely do we hear shock over a positive or even neutral response to a book. Okay, people sneer over The Da Vinci Code and the multiple Twilights, but when do you see an outright attack on a review recommending those books? It's not at all unusual, though, to see outrage expressed because someone pointed out some flaws in a fan favorite.
Why are we so put out by what we consider misplaced negativity, but we let misplaced praise roll off our backs? Critically speaking, isn't one just as bad as the other?