I, also, agree with the other editors. I believe that pohnpei stated it best when saying Diamond's theme is a "flavor of the month." It seems that people tend to find a niche that has not yet been fully explored (or only the surface has been scratched) and run with the idea. I also believe that, like accessteacher, a deeper examination of the ideologies and themes needed to be examined and would have been more beneficial to the text.
I agree with other editors. Although as a wannabe eco-warrior myself I applaud his emphasis on the environment and how this is one of the massive issues that will dictate our survival as a civilisation today, I don't necessarily think it is the only reason that dictates the survival or otherwise of societies, and I think that a more thorough examination of other factors would have benefited this book.
I have had my students read Collapse for a number of years; and am personally a bit concerned that he places the collapse of all the societies in his book on environmental irresponsibility. Societies have risen and fallen throughout history for reasons other than the way they treated their environment. He makes a telling point, particularly with the Vikings of Greenland, but at times is perhaps overly simplistic. I am not sure, however, that I would dismiss him as the "flavor of the month." He does raise some significant points well worth pondering.
The best critique for both Collapse and Guns, Germs, and Steel is that both are reductionist works. In one sense, Collapse is about how human societies "choose to fail." In another sense, Diamond seems to think the only choices that really matter are those related to wise use of resources. Everything else is superstructural or irrelevant. I am very sympathetic to Diamond's arguments in general, but I also think other factors can be important, even causal, when it comes to the decline of societies. Many people have also pointed to free-market successes in using limited resources, which seems to miss the point as far as I'm concerned, because we don't know how long these successes will continue.
You could certainly argue that his theme is just sort of "flavor of the month." Everyone is worried about global warming and he just happens to come out with a book that says societies collapse when we don't respond properly to environmental stresses. You could argue that it's just too convenient for him to "find" that out at this particular point in history.