Actually, it's on the nightstand and in the briefcase to read on the way to, from, and in China this week and next. The Wiki page has a few newspaper reviews, but I have yet to track down an academic one. The newspaper reviews there, including an interview with Indian Country which is the most interesting.
I have to wonder how much will be about the actual depopulation which seems to me to be the key issue. What is the evidence for it and what does the archaeology say about the distribution and density of population pre-contact? Seems to me a few years ago most of the conservative estimates put the loss at around 85% (see Vectors of Death by Ann Ramenofsky which has GOT to have the best book title ever). Ramenofsky based much of her work on her dissertation which compared archaeological manifestations both before and after contact. Population is certainly a dicey issue though and a lot of the literature tends to rely on. . . .ethnographic analogy, which is more or less what this book sets out to question.
UPDATE: I tracked down one review by Dean R. Snow in Science (Science 2 June 2006: Vol. 312. no. 5778, p. 1313 DOI: 10.1126/science.1128736). It pretty much tracks what some of the newspaper reviews have to say. Couple of passages (it's sub-only):
Along the way, Mann shoots down popular misconceptions that have been previously refuted by various authorities. I will cite just a few. . .Surprisingly simple hunting societies encountered in interior South America were the scattered remnants of more complex societies that had been devastated by epidemics, not pristine survivors from the stone age. Pizarro and Cortés defeated American Indian empires because they had guns, cavalry, and germs on their side, not because the Incas and Aztecs were hobbled by superstition and other forms of inferiority. The American landscape was an anthropogenic one for millennia, which reverted temporarily to wilderness between the epidemic decline in Indian populations and resettlement by expanding Europeans. Deep anthropogenic soils and other archaeological evidence in the Amazon lowlands indicate that before 1492 Indian populations were much larger there than previously suspected. The last finding was particularly inspiring for the author.
I bolded that bit myself, since this seems to be the overarching story of American archaeology, and world archaeology in general: that modern technologically simple societies, from the !San of Africa to the Amerindians observed by early European explorers are somehow evolutionary holdovers from an earlier time. Probably goes back to the idea of evolution as a ladder that was overturned by Darwin, but still lived on in anthropology via the various stages concepts (stone age, bronze age, etc., egalitarian, chiefdom, etc.).
Unfortunately the book also contains overstatements, errors, and speculations of the kinds that creep in when an author's purpose is to make a strong case for a thesis. Again, I will cite just a few. It is unnecessary to argue that Europeans were "unbearably dirty" to make the case that Indians were not filthy savages or to repeat Henry Dobyns's wildly inflated population estimates to make the case that colonial era epidemics were unprecedented in their devastation--everybody was smelly in 1491, and 60% mortality is horrendous no matter what the absolute size of the population. Older is better in popular books, and Brazil's Lagoa Santa skeletons are dusted off again. But none of the surprisingly early dates claimed for these and other finds in eastern Brazil meet minimum scientific standards for reliability. The Great Law of the Iroquois is very different from the U.S. Constitution. The framers of the latter were inspired mainly by European philosophy, yet Mann repeats the modern myth that the framers of the Constitution "were pervaded by Indian ideals and images of liberty."
Doubtless there will be a lot of this sort of thing, which isn't really surprising for a non-specialist writer and in a book of such scope (though the Iroquois thing seems a bit overdrawn to be a result of mere ignorance of the literature).
Snow sums it up:
The book is a good read. For the most part, Mann paints a fair picture of American Indians, and his account is largely free of fawning political correctness. But readers who know the subject well will question the polemics, erratic organization, and various factual statements. Critical readers should use 1491 only as a starting point, following the author's excellent notes and bibliography to explore more specific topics in the vast literature pertaining to Columbus's Other World.
That seems to be the general consensus. In the first few pages of the book I haven't seen anything to raise my eyebrows so we'll see.