An excellent to the point explanation of the theory of relativity without getting into all the nuts and bolts. It’s not very easy reading and not very easy theoretical descriptions. I had to read several sections two or three times over before it finally sunk in. But I think that was probably due to me and not to his explanations. I’ve read several of his books and this subject was the most difficult to understand.

Well I struggled through this, knowing that I'll have to read it at least twice to have any chance of getting my head round Relativity. I'm pretty sure no-one else could simplify it any more, Feynman was after all famous for his teaching and clarity of thought.

Feynman's writing captivating as always.

I won't lie, on first read some of the deeper topics were hard to digest (e.g. curved space-time, four vectors), and I would probably want to spend more time studying these topics more carefully.

Some of the most complex theories explained in a way that it's easy to grasp with limited Mathematics. Not saying you can breeze through the book. Some sections do require re-reading. But by the end of the book, you will have a much better practical understanding of relativity.

again one of those books that i reached for in order to get some insight into the whole quantum nature of electromagnetic phenomena and i obviously didn't read the description attentively enough, since it turned out that the chapters cover a wider array of physics than i thought. i didn't want to miss a chance to refresh my very feeble knowledge of physics so i gave it a go as a whole.

okay, first for the criticisms - feynman is (sadly) one of those physicists who thinks that having a nobel in physics suddenly makes him a credible authority to speak about anything in this universe, meaning he has no humility to abstain from generalizations about philosophy, psychology and religion. this always was and always will be in poor taste. secondly, as he admits himself, these lectures gained more traction because of who he was and not as much because they were really well thought out or broadly comprehensible; like many professionals, he is often unable to keep in mind what is self-evident, what is new and what "tempo" the explanation ought to have. less time spent on high school physics and some additional steps here and there would benefit his cause greatly, im sure. there is also some ambiguous use of language as he ventures into other disciplines, but okay...

in all honesty, and i dont do this often, ive only skimmed through some parts of this book (elementary particles, conservation of energy, gravitation) so im in no position to comment on those. the chapter that i read carefully - and the one where feynman is most "at home", the one on QM - is actually rather swell. both the math and the language are clear. i would have loved to hear more about the nature of the measurement problem and general decoherence, but it does seem that everybody avoids these problems like the plague.
a good book to have, will come back to it again when i have more spare time to ponder along.

One of those books I'd want to re-read each year

This has a few marked differences in comparison with its sister volume, The Six Easy Pieces. It's at a higher level than a pop-sci intro and so it expects its readers to have seen some physics before and it has quite a few equations which means you will need some knowledge of vector algebra along with basic integral and differential calculus to fully appreciate the content.

This book deals exclusively with Einstein's theory of relativity (both special and general) along with a brief detour into the topic of symmetry of physical laws. Although Feynman does a brilliant job of explaining this unintuitive and fairly involved topic with the aid of helpful albeit quirky examples and analogies, I only got a vague sense of Relativity and its consequences. I felt the book was too short to include all of the 'whys' and 'hows', which made things a tad confusing for me. This is after all bits and pieces of Feynman Lectures strung together to introduce a wide audience to Einstein's groundbreaking ideas, so don't expect to understand the topic well enough to be able to explain it to someone else.

That being said, I do think reading this book will stand you in good stead when you move onto more technical and thorough (including the complete Feynman Lectures themselves) books on the topic. Recommended for Physics enthusiasts.

I really loved this book.

I have studied relativity in university, and afterwards, read several books on the subject, including Hawking books, but I have not really felt that I have started to grasp what general relativity's consequences are, until I read this book.

The meticulously crafted analogies and examples gave a new meaning to symmetry in physical laws, the physical consequences of relativity, and the geometry of space-time when it comes to how I think of them.

There were a few locations where I felt sudden jumps over ideas, but I guess that is natural, as this book is selected chapters from the complete Feynman Lectures, which I am hoping to go through in whole someday.

Insight for non-mathematicians

I've often wanted to understand how mathematics has been used to define laws that are proven, or not, by experiment.

I can understand how experiment can find the mass of an electron, for example. But how can a series of equations predict the mass?

This book provides just such insight without a lot of heavy mathematics. You should brush up on basics of motion and the calculus of derivatives to make the most of the book, but it's really not required.

fascinating, revealing perhaps the best of Feynman. A delightful volume, provides a unique glimpse into the mind of remarkable human being.

Review:
The book was a little bit interesting, I learned some new concepts. It was a little bit dry for me, with too much calculation.
Main points:

vectors - the laws of physics are symmetrical for translational displacements
we can add and subtract vectors
the laws of physics are not unchanged under a change of scale, this was discovered by Galileo, you can’t scale everything up and down
Newton - The motions of bodies included in a given space are the same among themselves, whether that space is at rest or moves uniformly forward in a straight line.
space and time are two properties of an object, they are not two different properties, but a mixture
analogy: width and depth
four vectors: three of momentum and one is energy (time)
space and time are curved near heavy objects
We define a curved space to be a space in which the geometry is not what we expect for a plane, going in a straight line on a sphere

This is not easy reading if you're not a physicist or a mathematician. You can likely make it through it and learn things even if you have difficulties with the math. I found it worth the trouble even when it made my head ache.