Can't buy it here in Czech Rep., so I am downloading the audio version. I've read Guns, Germs etc. which was interesting. I don't think he answered all the questions, however. He explained why certain societies developed faster than others, but he didn't explain why some agricultural societies evolved slower. For example, he didn't explain China's or India's stagnation in comparison to European technological boom. He also didn't explain why certain cultures remain narrow-minded and refuse to modernize while others have overcome this problem.
I agree with the first criticism, except to point out that he did mention the fact that 500 years ago Europe was a backwater and China and especially the Islamic world were the most advanced, before going on to attribute the shift in fortunes to random historical chance and pointing out how China might end up more dominant in the future.
He could have spent more time exploring those two issues, but they weren't really on the level of analysis he's shooting for as they're too narrow and specific. The second criticism in particular is basically something he assumes as a natural variable and therefore discounts as a highest-level explanation for inequality: Some cultures are more open to change than others (remember he illustrated this with the contrasting attitudes of different New Guinean tribes to new technology diffusion), so what matters is how many cultures you have in a location, to maximise the chances of progressive ones to diffuse change once an innovation happens, which means population size and density are important factors as are the ease of diffusion.
I think you can apply the same thing to the other criticism about Europe, China and India. He
does regurgitate several old post facto geographical explanations for differences within Eurasia, such as the ecological fragility of the Fertile Crescent being a long term disadvantage, and the old idea that a unified China was at a disadvantage compared to moderately fragmented Europe using the burning of the Navy as an example of how progression could be shut off easily (China was controllable by one government which could reject change, Europe was too competitive for that).
But honestly, those explanations are of a different nature than his more sophisticated analyses of ecological factors at a continent-wide level - when he gets more specific, they're simplistic geographical determinism, and they're old ideas, and they're made better elsewhere. I think the whole "once you get more specific than Eurasia, ecological determinism ceases to be absolute" argument implicit in his work and occasionally specifically stated, is more effective than when he
tries to get more specific.
Besides which, a long view of history reveals that Europe wasn't eternally and naturally dominant, it has just been so for a couple of hundred years. In the long view the centres of domination have moved all over Eurasia.