I do find his works to be Anglo-centric and generally forgiving of British military tactics. What I am more worried about is whether his understanding of older battles such as Agincourt are more speculation or based on fact. From what I have seen, he references chroniclers and witnesses of battles; why does he and why should we assume that their perspective isn't biased, or is knowledgeable at all? If someone could enlighten me on the validity of their perspectives as well, I would greatly appreciate it.
I liked it. I am most interested in his analysis of cavalry charges, and everyone I've talked to tend to support his suggestion that cavalry is basically a psychological weapon. I don't know much about the specifics you've asked for, but I've never run across anyone that said Keegan was wrong.
I would suggest you reconsider your notion of "bias." Bias isn't bad. It can be quite useful. I prefer to call it something like "lived experience." Bias helps you understand why people wrote what they wrote and thought what they thought; and if history had no moral or subjective purpose I'm not sure why we would bother with it. The point is to try to understand other people, and if that means trying to understand Hitler, you can disagree with his actions all you like, but the point is to understand (not to in any way suggest Hitler's crimes should be forgiven - I'm only saying one should be able to clearly describe Hitler's reasons).
You can take something like Mein Kampf and say it's biased, or you can take it and say it is representative of a real, lived experience. I suggest you learn more from the latter.
Also, I know I Godwined myself.
OK, for starters, having read the book, I would say that personally, I enjoyed it and found it to be well written and also in-line with my existing knowledge. As for what those with a bit more of the latter have to say on the matter, I fired up JSTOR and found a few reviews of the book from when it came out.
Writing in the The Journal of Modern History, Vol. 49, No. 4, Dec., 1977, John Mundy praised it as a good, fun introductory read to military history. He of course has his criticisms - Keegan is "unpleasantly kittenish" in his attitudes towards the non-British, and finding a general detraction from the quality of the book due to the Britishisms - but in the end is very positive, noting that "Keegan's chapters on Agincourt, Water- loo, and the Somme remind us that the history of war is not only about command decisions or the economy and sociology of warfare but also about killing and dying. We need this because our liberal tradition of history has veiled our extraordinary gift for slaying each other."
The second review I read is by John Beeler, in The American Historical Review, Vol. 83, No. 5 (Dec., 1978). Beeler is also very positive towards the book, opening his review with about as praisful a passage as you can have:
"Old, Unhappy, Far Off Things," the initial chapter of John Keegan's The Face of Battle, is "must" reading for anyone with even the remotest interest in military history.
Really, you'd think that Beeler was being paid off by Keegan. "Thoughtful and unusually perceptive", "symphony in prose", "masterpiece", "could not be put better than this"... The accolades just keep coming. He notes a few criticisms, but also excuses them, such as in the case of Agincourt, which Beeler finds to be a little lacking, but notes that it isn't Keegan's fault correspondence doesn't survive from the soldiers who fought there.
So, there you have it. I would say that the reviewers, or at least Mundy, shares your concern about Keegan's Anglo-Centrism, but in the end, the consensus is that it is a great work.