Part of the reason it took me so long to read Mann's book is because I know so much about its subject. Prehistoric ecology was my daily fare for fifteen years of work (in both academia and "cultural resource management") in North American archaeology. So I felt compelled to check pretty much every endnote (and there are forty pages of them), along with many of the bibliographic references (another forty-five pages) in 1491. I have to say that I am extremely impressed with how well Mann balances current scientific and historical research and the often arcane jargon of anthropological archaeology* with the remarkably readable popular history (and prehistory) presented in his book. Balancing the nuances and complexities of this research with stories that can keep general readers not only awake, but thoroughly engaged, is pretty damn hard. Mann makes it look effortless.
His well-researched book is basically an overview of several American Indian societies (and some of the archaeological and historic research regarding them in the last few decades), mostly in the period before Columbus's arrival 515 years ago. Of course, this is a huge span of both space and time, and a monstrous amount of research. There is simply too much North and South American prehistory and ethnohistory to fit into any book, even one the size of the Oxford English Dictionary.
So Mann picked some of the stories that he found most interesting to relate. He jumps from an account of John Billington's sons** and their adventures after they disembarked from the Mayflower, to Squanto (aka Tisquantum) and his political machinations, down to Lake Titicaca and the Inka empire before Pizarro, up to the Aztec capital of Tenochtitlan, lingers a bit on the origins and importance of maize and cotton, then returns to the remarkable Mississippian chiefdom of Cahokia (near present day East St. Louis) from 800-1200 AD, then jumps down to the Amazon basin a thousand years ago, visiting Olmec, Oaxacan, and Mayan cultures along the way, and then finally comes back again to historic times and the Iroquois Nation. It is quite the whirlwind tour, but Mann ties it all together admirably.
Readers who think of prehistoric Native Americans as timeless inhabitants of a sylvan paradise who "lived lightly on the land" will find much of Mann's book eye-opening. Those who assume that these cultures were not very populous, don't appreciate their diversity, and have never heard of the devastating diseases that followed the "Columbian exchange" or encounter may find the historic accounts of epidemic death in the New World more shocking than those imagined by Stephen King in The Stand.
Since I am familiar with the literature and research behind the book, I was also more than a little dismayed by how many reviewers said they were just blown away by it. They were shocked not because the book is so well-done (although it is), but because that they had absolutely no idea how radically some Native societies altered their natural environment, or because they'd never heard of Cahokia, or they didn't know how egalitarian the Five Nations were, etc. This unfortunately shows just how poorly my former colleagues manage to share their work with the general public. Which is not good for either archaeologists (most of whom depend on government funding at some level), or for people who are reading ideas about American history and prehistory that were out-of-date a generation or two ago.
So - Mann's book is definitely long overdue. But there is still a lot of room left for popular yet not overly simplified works that could help fill the huge chasm between college archaeology textbooks, American Antiquity articles, and reworked dissertations (which leave a lot to be desired in terms of "readability"), and the brief, often inaccurate snippets on archaeology that appear in newspaper and magazine articles. A few years back, I did read and enjoy Sharman Apt Russell's When the Land Was Young: Reflections on American Archaeology, which presents some of the controversies and the colorful people engaged in archaeology (though in a highly "edited for prime time" fashion), and I recommend her book, too. But there's still so much interesting research being done out there -- there's room for a lot more books like 1491. Maybe someday I'll try my hand.
PS Mann's book has an excellent index. I thought I should mention that, since I've ranted here about a lot of recent books that don't include indices.
*Readers who would like an introduction to modern approaches to anthropological archaeology (and some of the language you need to understand the academic literature) may want to check out Adrian Praetzillis's Death by Theory: A Tale of Mystery and Archaeological Theory.
**Like Charles Mann, I'm also descended from Mayflower passenger John Billington, who was executed for murder in 1630 (the first person hung in the Plymouth colonies). I found Mann's endnotes on Billington particularly interesting, as I had previously heard the story that this non-religious "Pilgrim" was framed, but hadn't heard the arguments behind the Puritan conspiracy theory.