Yes. Both positive and negative experiences can be helpful to other consumers so long as your reviews are honest and provide as many of the relevant details as possible. Your opinions are generally protected, but posting false information can have legal ramifications.
Everyone gets a bad review from time to time. Chances are, one bad review will not hurt your website, as your happy customers or users will soon write good reviews. We often find websites that have one or two bad reviews to go along with their good ones often will get more traffic and customers. If you are affiliated with a website and would like to respond to a review,