Is the IQ test really a big hoax?

I was just thinking about how IQ tests are so highly regarded, because I have always believed there is really no definite way to test how smart an individual human being is. I mean, Marilyn vos Savant scored a 186 on her IQ and Einstein scored a 160, even though he had far more superior knowledge than she ever did. I believe how smart you are is determined by the amount of facts that you know, and believe that there really is no way to test your knowledge on everything. What do you think?