1491 is not a worldshaking book. But it does shake up one's world view. I know not everyone will agree with its viewpoints that civilizations in the Americas were more sophisticated and accomplished than we previously thought.
Mann lays out the evidence - archeological, genetic/biological - as well as the historic context of trying to link Native American civilizations to more 'accomplished' civilizations. He also paints a vivid (though far from idyllic) picture of life before and during the initial contact with Europeans.
I've read it twice and will read it again. Its a good one folks - go out and lay hands on it and the books in the bibliography.
Great book - Of course, covering 13000 years of the history of 2 continents can't be anything more than a survey. Very dense (at least by the standards of the books I read), it took me 3 months to read. Makes a stab at showing both sides of all controversies (and there are many), although he comes down on the side that there were more people in America in 1491 than previously postulated.
As a Native, The first part of this book really made me angry, because it makes perfect sense as to conditions as the Europeans came and took over this country. I had the history of the Conquistadors when I was a child in southern Cali. The spanish-enhanced version of the conquest of central, south and north America is somewhat different from the truth. After the initial shock from the beginning of the book, the rest reads well, is articulate and makes very valid points as the the real history of this Indian Country. I totally recommend this book to anyone interested in a better version of things than the "noble savage" stories of Native Americans currently spewed in today's schools.