Using the internet to rate your professors is like using the internet to check the symptoms of a mysterious illness. You’ll get a lot of information, but probably not a whole lot of clarity. You’ll almost certainly come away with more anxiety than when you started.
Keep in mind that Ratemyprofessors.com, like any website that allows customer reviews, is more likely to be inhabited by unhappy people. Happy people don’t often bother with reviews — they just get on with their lives.