All kind of artists--writer, painters, musicians, etc.--are potential targets of critique. Remember: beauty is in the eye of the beholder. Thus, your work may both appeal and repeal people. Not only on TNBW, but also once it's published. Just look at the Amazon reviews. There are always chaps who think your story sucks just because, as well as chaps who find it cool without any reason for.
Granting that all critiques in TNBW are candid, not all reviewers are professional enough. Some think that, by being blunt, they are doing the writer a favour, for then the writer will easily realise her flaws. Others are so polite and subtle one ends up wondering what was exactly what the reviewer meant. Within those boundaries, each writer must decide what is valuable and what is not.
I wouldn't be concerned because of a one-time reviewer who randomly picks one of my chapters and pours vitriol over my story. Without context, even the best King's English may be mercilessly nit-picked, and a lose Romeo and Juliet scene considered an anecdote about two stupidly eager teenagers. However, I'd be concerned if several of my reviewers, who have been following my story and are well aware of the plot, point all at the same weakness. It would be amateurish to turn a blind eye towards such shared observations based on the conceited belief that "only my opinion counts".
TNBW is not free of opportunistic point-gatherers who review at random, seldom providing meaningful advice. Either it is merciless or excessively flattering. That kind of review is easy to spot and discard.
Other problem that may happen is that your work may be reviewed by people who, in an effort to help you, are reviewing a genre they don't enjoy. For example, I'm not fond of Erotica. I found explicit descriptions of sexual intercourse disgusting. Thus, my reviewing of stories within that genre would must likely be biased by my personal taste, even if I try to be candid. The best is to partner with writers working on your same genre. You may think it might bias their reviewing the other way around, finding whatever you write--or vomit--awesome. While it might be true, it's also true they are better qualified to judge your work only because they are into the genre. Moreover, once published, the likelihood is that your book will be purchased by readers fond of your genre, not the other way around, meaning that it is with genre-fan eyes that your work has to be reviewed.
A personal example: once, another writer from TNBW started reading my YA story "Where Heaven and Hell Meet". She started to point out at what she considered a large number of plot flaws that are givens in YA literature, like the absence of adult involvement, teen angst, wrong decisions, etc. After reading four chapters, she told me she was not "liking the story at all" because she actually considered young adult stories, in general, "simple-minded and lacking a true message." Of course, she stopped reviewing it. Had I despaired because of her harsh reviews, I would have dropped the story and possibly my writing as a whole. I realised she was not the right reviewer if she hated young adult literature and considered her comments with that grain of salt. I took few of her observations--there some worth being considered--and rejected the rest of them.
Hope the above is useful.