This book was written as a prophecy about what the author felt would characterise the C21st. Now that we are nearly a decade into the C21st, we have the ability to look back and see if he was right. If yes, then this book was prophetic and its lessons should be learned. If not, then he is wrong, and the book is little more than an airport novel.
On one or two dimensions, Huntingdon has been extraordinarily accurate, predicting that Islamic extremism would become the number one security threat to the West in the C21st. Ominously, he predicted that the West would be driven to attack nations that possessed WMDs in the fear they would pass them on to terrorists. This is the Bush doctrine, written before Bush was even an elected official, never mind President. Equally ominous, he predicted that Islamic radicals would rally to the cause of any Muslim state attacked in such a way, and the influx of foreign insurgents into Iraq confirms this. Interestingly, the author predicts that the Taliban and Al Qaeda would be very prominent in the C21st, yet never actually names the organisations by name (in the case of Al Qaeda because it did not adopt its current name until several years after the book was written).
Huntingdon is slightly inaccurate in his prediction that China would become more bellicose and confrontational. At least so far, China has been warm towards the West, with trade deals and cultural exchanges flourishing. Another weakness of the book is his rather arbitrary definition of societies, and his notion that a "core state" would drive forward its respective civilisation. This is not the case, with supra-national agencies taking the place of "core states".
Overall, the book is highly recommended. However, given its relative age, it would be advisable to buy a more recent book on geopolitics as well, to top up the introduction that this book provides.