I had long heard of Feynman's great ability at science communication, and reading this book, it's not hard to see why: under one cover, he weaves together fairly complex ideas concerning vectors, special and general relativity in such a simple, yet nonetheless scientifically accurate way that you find yourself saying "Aah, I see; that makes sense." His style is unlike any other communicator of science I've ever come across: he presents ideas in a simple, straight-forward, context, and it all flows very well form one chapter to the next, yet he doesn't loose any scientific accuracy in the process; moreover, he enhances your knowledge of physics, adding fresh new insights and connections which you'd never realised before. Too many scientific journalists these days get so obsessed with making topics seem as simple as possible, they loose their true essence; Feynman's insights are like a breath of fresh air.
As far as the background of the reader is concerned, I'd reccomend the reader to have a maths and physics education up to about A level/IB standard, if they really want to appreciate from Feynman's fresh new insights: though he does build everything more-or-less from scratch, basic knowledge about calculus and physics equations are assummed. Furthermore, I can imagine the more general reader getting a bit bored with this book.
Overall, a great read if you're interested gaining a fairly detailed understanding of basic relativity.