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.