I read Guns, Germs, and Steel some years ago, but don't remember much from it. I thought is was interesting and entertaining, but Diamond didn't have anything particularly interesting to say about his core question: How did the West came to dominate the rest? Here's how Oliver Burkeman characterizes Diamond's argument in The Guardian:
Guns, Germs and Steel began by repudiating the obvious, racist answer: that Eurasian peoples won out because they were smarter and more vigorous, down to their genes. Instead, it was a matter of geography. Europe and the Middle East had good soil, plenty of easily domesticable animals and plants, and a main axis running east-west, instead of north-south – meaning that crops, livestock and tools could spread easily, without confronting big changes in climate or day length. The world’s first farming societies emerged, leading to bigger settlements and concentrations of political power. Meanwhile, humans living among farm animals developed immunity to the diseases they carried. By the time they encountered other societies, their military power, metal tools and, above all, their deadly germs gave them the decisive advantage. Diamond’s books feature few intrepid explorers or brutal colonisers; rather, there are just accidents of geography, and their after-effects.
The fact is, in a sense, the Eurasians were smarter. But not through superior genes. It was a matter of culture, as I argue in The Theory of Cultural Ranks at 3QD. Diamond has nothing comparable to propose. His argument amounts to saying that geography gave Westerners more time to think. But it says nothing about what made that thinking so devastatingly effective.
He's assuming that, given enough time, more effective ideas inevitably show up. Not only do we need to see an argument on that point, rather than tacit assumption, but Diamond needs to say something about just what makes for more effective thought. He says nothing about that.
Which is to say, he managed to write a big entertaining book that simply failed to address the question he set out to answer. The anthropologists are right to say that geography isn't much of an answer. Alas, I rather doubt that they'd like the answer I propose any better than they liked Diamond's.