I want to start a product review website, what are the legal ramifications?

Your major concerns are (1) defamation, and (2) some type of business tort, such as unfair competition, interference with prospective business advantage, etc. Defamation cannot be based on opinion. By clearing identifying your product reviews as opinions, you are probably safe for favorable and non-favorable reviews. Of course, one cannot "bless" what one has not seen, and certain close judgment calls might justify running it by an attorney. Busiess torts are far less likely. They tend to arise when the test proceeding are "fixed" like trying 10 times to tip a SUV on sharp cornering until you finally get it to tip by going in exces of legal speed limits. If you don't fix the results, you exposure is probably very limited. Again, each factual situation my have a different analysis, and that's why newspapers and television stations have attorneys on their staff.