Why am I always late to the party?
It's okay, I was to.
But let me add my own thoughts, anyways. Do note it's been years since I've read Diamond, so some of what I say below may be off - feel free to correct me.
While I disagree with a number of Diamond's arguments, as someone who is strongly against Eurocentrism, I personally believe he does have good intentions and is, even perhaps, a bit admirable in his attempt to dispel common Eurocentric beliefs. here are, anyhow, still academics like Niall Ferguson who claim to adhere to these ideas, and in mainstream pop history these ideas still remain well and alive - so in that sense I can admire Diamond for his attempt to dispel these. The problem is that he often unwittingly relies on outdated Eurocentric ideas such as the idea that Europe has a "perfect" temperate climate (disproven by the fact that advanced societies have developed virtually everywhere except the extreme cold climates) or the Orientalist assumptions of Asiatic states being gigantic despotic blobs - both of which have already been mentioned in this thread.
I think Diamond's main issue is that he tackles everything in such broad strokes that he ignores the specifics and peculiarities of each specific situation. In a sense, he is describing history as if it were a game of civilization: a clash between well defined entities rather than a truly messy diffusion and mess that history really was. (Granted he does appear to say (Western) Europe was factitious, but only within itself) In a way I also feel as if he describes technological advancements as if they were as simplistic as Civ tech trees or something. Anyhow, for instance, when it comes to the Spanish conquest of Mexico, if I remember correctly, he completely glosses over (or mentions briefly but doesn't expand on) the fact that Cortes had 200000 native enemies of the Aztecs alongside few hundred or so troops. Or, as mentioned previously, he completely ignores the many disunited regions of the world, politically and geographically - SE Asia, India, Japan, West Africa, the Middle East, etc.
I suppose we can say this is largely due to the fact that he is not trained as a historian. I guess a historian or someone who has some experience dealing with history wouldn't make these sort of generalizations, or not make them without addressing exceptions and specifics. And ultimately the problem, I think, lies with the broad sweeping generalizations, and trying to make specifics into generalities.
Anyhow, I am agnostic as to whether it was inevitable that Europe would come to dominate the world, or whether there was indeed some sort of European or Eurasian "miracle". What I am certain, though, and something I think Diamond also glosses over, is the fact that economically the world was still centered around India and China until the Industrial Revolution.
Or something. I dunno. This is a very complicated topic.