This is a book which has had wide currency among international opinion-formers. The egregious Tony Blair has cited it many times (typically enough, without actually crediting it as such, just using the words as if the product of his own thoughts). My problem with it rests on some inadequacies of expression and treatment. The role of race is virtually ignored for one: Islam only attracts those in or descended from certain racial or sub-racial groups, where Islam has been predominant for centuries. Yes, there are a few mavericks and cranks who take it up, but these are rare exceptions. So Islam is NOT (as Huntington claims) likely to somehow take over the "West" EXCEPT by conquest, destruction or (most crucially) by Europe and elsewhere accepting vast numbers of Muslims (who have, as he says, a far higher birth rate) into the European or European-founded societies. Unfortunately this IS the case as Europe is flooded with infiltrating millions.
Huntington's view of "The West" is very Americo-centric. Instead of seeing our Age (I.E. the 2,100 years after 1415) as a whole as Anglo-American-German, as Rudolf Steiner did (he called it the "5th Post-Atlantean"), or as "the age of the white northern European", Huntington really thinks of America as the heartland of Western Civilization (and not, as some might, one of its graveyards!) and thinks that if America ceases to be "Western" by giving up individualism, the Christian church(es) etc, then America itself will be "de-Westernized" and the West would be "reduced to Europe and a few lightly populated overseas European settler countries [and] becomes a miniscule and declining part of the world's population on a small and inconsequential peninsula at the extremity of the Eurasian land mass" (paperback edition p.307).
This above viewpoint must be seen as absurdly misconceived and "little American". For one thing, even Western Europe has a population at least equivalent to that of the United States and its Canadian appendage. And some of the overseas offshoots of the European Empires (especially the British) have large populations which are still mostly of European descent, such as Australia, which is now counted as having about 20 million. And what is the obsession with mere numbers? The British ruled most of India and Africa and elsewhere with tiny groups of British/European civil servants and officers disposing of modest numbers of European police and soldiers.
To my way of thinking, the book is important because it does raise the subject, but apart from the above criticisms, it fails to note that in advanced sections of European (or, as Huntington would put it, "Western") humanity, there is a continuing evolution of consciousness which might lead to a quantum leap in civilization, particularly if Europe joins with a fully independent Russia, that is a Russia which is run by Russians and not "rootless cosmopolitans" with Russian passports. That Europe + Russia could be at least the foundation of a a REAL New Order over time!