I don't think anymore words needed to describe this greatest work of all time! Pricipia is difficult to read, that is no doubt. But the impact of this book and its consequent influence to our world will never and never be overestimated. With the advent of Principia, our world will never be the same again! Even with the advent of relativity, I don't think there is hardly any scratch on this book. As the activities of our daily living and even in astronomical field, except when the speed of an object is approaching light, Newton's law is still the prime theory to govern it! Actually this book should be rated as 10 stars! In fact this book needs not to be rated!!!!