I recall an eye opening experience as a student, reading Feynman doing a calculation, of a planetary orbit I believe, by "integral calculus". As a math major I had just had an honors course where of a function on an interval was defined as integrable if for every epsilon, there were upper and lower step functions for f whose simple integrals differed by epsilon, and I could not calculate anything.
To my shock, Feynman showed that an integral is essentially just a process of adding things up, and he proceeded to compute, or maybe approximate, one with his bare hands.
I thought, gee, is it that simple?
The main objection I have to most of the posts here warning people away from Feynman is they assume that a book should only be consulted if it is guaranteed to help you pass some standardized test, and if not it should be avoided. I used to think some of the Fields medalists I heard were poor lecturers, but eventually I realized that learning a subject is an infinite job, and that one needs all the help one can get. The insights of a genius are just not to be missed, no matter how much is left out. No matter how naive or dull you think you are, you will likely be benefited by hearing the words of a master. I recommend you do not miss it if the chance offers.
But space tiger has put it most clearly (for most of us) in post #21.
[Oh and by the way, that honors calculus course was also taught by a genius, even if I did not learn to solve problems in it, and I would pay a lot if that course existed today in book form.)
I agree however it is often wise to consult many books at many different levels, especially if you are a beginner. I.e. read both the books you think you need, and can understand, as well as the ones you think you should read, and aspire to understanding.
And make up your own mind about a book. I once avoided a famous book because someone told me it is was hard to read. I at last was forced to consult it and found it clear, deep, and extremely useful. When I went back to the person who ahd discouraged me it turned out he had never read it and was quoting another person. That person too turned out to have been misquoted, and had never said the book was hard, merely "tedious", as it had too much detail for his taste!