Having seen both "Patriot Games", and "Clear and Present Danger", I found it easy to imagine Harrison Ford, Karen Archer, and Willem Dafoe reprising their previous roles. Given the critical and box office flop that was "The Sum of All Fears", maybe Hollywood should have tried to adapt this book for the cinema instead.
The circumstances of Ryan's elevation to the presidency were remarkably prescient, given 9/11, and the passage describing Saddam's assassination, and the religious motivation for it, was especially well written, if a little dated. Perhaps Clancy's crystal ball let him down on this one. He takes an almost pornographic interest in military hardware, but you cannot accuse him of not doing his research.
Where the book falls down is that, as the book unfolds, you can never be in any doubt that however much crap is thrown at the US of A, truth, justice, and the American way will always triumph in the end. The idea that someone like Darayei might think "Let's take on the world's biggest superpower, they're bound to take it lying down." is, frankly, laughable.
Overall, a gripping read, and I zapped through it whilst on holiday.