Most published reviews are positive, and that's nice.
Some negative reviews are written by people who are clueless, vindictive or have not even read the book they are condemning. If you write a book, it's important that you regularly check for reviews. Good reviews can be used to promote your book. Unjustified bad reviews have to be dealt with.
A while ago I discovered a review of one of my books on Amazon. It gave me the minimum one-star ranking and said my book must be terrible because it did not have a "Search inside the book" feature (as if I was hiding something). There were a few other meaningless complaints which revealed that the reviewer had never read the book. I assume the review was from a writer I slammed on this blog. (I don't put negative reviews on Amazon to minimize the chance of a flame war or pissing match.)
I complained to Amazon, and the review was deleted within a few minutes.
Another time I was criticized because the typeface I used was allegedly too big. I responded that the 12-pt type I used is the size specified by the U.S. Supreme Court to insure readability of court documents.
And another time one of my books was criticized for being out-of-date. I responded that the reviewer bought the wrong book, and should have bought the replacement book. I even offered to provide a freebie.
Set up Google alerts for your name and your book titles. You'll get automatic notifications so you'll know what's being said about you so you can respond appropriately. WARNING: be restrained when responding to negative reviews. Don't get into online pissing matches that may alienate potential readers.