Tracing the spread of human culture, language, and empire
Diamond traces the spread of human culture, language, and empire-building across the globe in terms of "geographic determinism"--a pejorative term he deplores: ". . . Societies developed differently on different continents because of differences in continental environments, not in human biology."

Specifically, he traces the ultimate causes that some human societies who (literally and sometimes figuratively) developed guns, germs and steel were able to subjugate the continental areas of the globe: domestication of plants for food, domestication of animals for food, transportation, power, and military purposes, and east/west continental axes that enabled food production techniques and the resulting political organization, language, and technology to spread most quickly.

Diamond makes a compelling case in a way that takes the racism out of much of the "manifest destiny" writing that surrounds this topic. Doing so, however, he takes a purely evolutionary view of human history. No allowance is made, for example, for events such as a single point of creation, dispersal of language from Babel outward (even though it would address a mystery he is unable to solve), or a world-wide flood which wiped out existing patterns of human dispersal and restarted human history from another single point.

so good I bought it for a friend
This book is interesting for those who prefer non-fiction. I bought this book for a friend.

Long Winded. Dull. A Waste of Your Time.
Without a doubt, this has got to be the worst book I have read in a long time. What would have been an interesting blurb in the sociology section of 'Time' magazine, becomes hundreds of pages of pure mindless dreck in the hands of Jared Diamond. Let me save you a few days of your life by summing up the book: The reason why white, western / European societies flourished and the rest of the of the non-white, non-western world did not was because the European climate and terrain favored domestication of plants and animals while the rest of the world's terrain and climate did not. Therefore, western man had more free time on his hands to invent stuff and put a man on the moon, while the rest of the world, to this day, is still screwed up. Wow. I am so annoyed I read this book and wasted so much time doing so.

Great for classroom teachers
While this book is difficult for many high school students, its ideas and the methods used to create his thesis are concepts your students can get. This would be a great jumping off point for an interdisciplinary unit and as the years go on, history and social studies teachers need to change the way we present history if we want students to be ready for the 21st century. In a time when students can get facts right off of Google faster than we could give it to them, we need to teach history as concepts and not focus on students learning only facts. Diamond interprets the facts to create a a thesis on why certain societies excel and come out on top. You could compare and contrast his thesis to the Human Web or the Kennedy's Rise and Fall of Great Powers. On its own, GGS could be a powerful tool in the classroom and teachers of all disciplines should read this text. All texts are biased and no one should expect perfection so if you want to be convinced of one particular view then you shouldn't read it. But if you are open to learning more and having more questions when you are finished (which is not a bad thing), then you should read this and give select passages to students.
For non-teachers, this book really makes learning history easy and interesting which may be different from your own educational experience.

A tour de force that isn't as biased or presumptuous as some critics have claimed
Many reviews claim this book to be biased and bereft of some important additional components that have influenced human evolutionary history. Diamond actually does mention many of these components, but seems to think they're merely subsidiaries of the broader agents behind history's patterns (which he lists as government/religion, germs, writing, and technology).

This book isn't perfect, but it's a great start and leaves the door wide open for those interested in pursuing the study of human evolution. It's boldest claim is that geography was the greatest SINGLE determinant of the evolution of human societies (continental axes, climate, biology, geology, etc.). He doesn't claim geography did it all and does indeed discuss important other factors such as cultural receptivity to new technology, progress, and change. But I think it's interesting that he goes so far as to claim that the essence of it all is mere geographical location, and from that simple starting point our many complex differences have spawned.