"Getting to Yes" introduces the reader to the basic mechanics and methods of negotiation. Having read the book you should have an overview of the most common strategies and scenarios of most negotiating situations: how to deal with stronger or weaker counterparts, what if they play dirty, establishing your and their alternatives, overcoming personal differences etc.
The underlying principal is to negotiate in a professional way, guided by verifiable facts, fair rules and respect / trust. The book illustrates by a number of examples the benefits of such "principled negotiation."
Most proposals will seem quite familiar and common-sensical to most readers, the strength of the book is however to put them all together in a coherent and concise volume. Will it make you a super-negotiator overnight? Doubtful. But it might - and did for me - make one more conscious of how we actually negotiate, and why we succeed and fail.
I have one major criticism about the book though: It is based on the first editions, which have been left unedited. After the core text the authors have added a series of questions and answers they have been set about the book. A new edition would have deserved for these points to have been incorporated in the text, so that you can re-read a single section and have all the text at hand. This is just sloppy work in an otherwise good book.