Before posting a web hosting review one has to be extremely careful since Internet is an open space and anybody and everybody can read your messages. The reviews you right would not only reflect the quality of service provided by the webhosting provider but it would also have a reflection on you as a customer. Many bad reviews from you about various web-hosting providers will reduce your reputation as a genuine reviewer. It makes a lot of sense to carefully evaluate your reviews before hitting the post button. In addition, since most providers will have something good and bad about them if you decide to submit a negative review make sure you give something good to their credit also.
Any good you do to them will surely reflect on you and remember nobody is perfect and a web hosting company is surely not. They are limited by the limits of technology and we need to recognize that. Having said that, do not hesitate to chide them for cases of gross neglect. Gross neglect is simply inexcusable.