As the title states, this is undoubtedly the worst book Clancy has ever written, and as I say that as someone who generally enjoyed his work.
That's not to say it's entirely without merit, but it has numerous flaws that make it the last book of his I would recommend.
First off, it's obvious this book had little to no editorial control. In earlier books, Clancy tended to hammer home points repeatedly and occasionally bash people over the head with the points he was trying to make, but it was all relatively restrained to the amount in this book, and the streamlining of this content alone would likely have reduced the page content by a full third.
Second, Clancy once remarked he was surprised how well "The Hunt For Red October" sold considering it didn't include any sex scenes, and the one in this book is pretty cringeworthy. I've read much worse, mind you, but erotica was not Clancy's strong suit, and I'm pleased to say he never dipped his toes in this pond ever again in any future stories, which, given the wooden dialogue and attempts to sound erotic that sounded like bad lemon fanfic written by a eunuch, is a very good thing.
Another problem is that Clancy's contempt for Communist China doesn't even try to be remotely subtle, which, given he portrayed many other cultures with a reasonable amount of respect for their backgrounds despite his own publicly stated opinions on them, is quite blatant. He shows extreme contempt for their abortion policies and goes to absurd lengths to paint them as horrible people for them, even after acknowledging they do and still have legitimate overpopulation concerns, and in interviews about the book he confessed he didn't even try to hold back his contempt at all.
On a related note, the Chinese antagonists are portrayed as completely stupid. While Clancy occasionally made his antagonists stupid in previous books, it was usually for understandable reasons, such as Daryaei in Executive Orders being insular and not understanding American politics and culture as well as he thought he did or the Japanese, while reasonably competent, were made complacent because they thought they knew what to expect the whole time in Debt of Honor.
By contrast, the Chinese act foolishly at every turn in this book. They proceed with trade negotiations by making total asses of themselves the whole time despite needing to swallow their own pride a little for practical reasons, and still do this even when it's clearly backfiring. They proceed to go to war with Russia even though the US, NATO, and Russia join forces very openly to give them pause, then proceed to run the brief war very incompetently, to the point Hitler's siege of Stalingrad looked like sheer genius by comparison.
This is quite bizarre given how the Chinese antagonists were portrayed as being able to show a considerable amount of guile and foresight in the preceding books.
These points aside, the rest of the book is not too terrible, remaining reasonably accurate on most technical grounds and retaining Clancy's trademark attention to detail, but unfortunately the pacing of the book means the bad parts are often back to back with the good parts.
Overall, if you're a die hard Clancy fan, it's still worth reading, and a later book by Clancy does its best to attempt to salvage the worst parts of this book, with a decent degree of success, so if you can stomach the cringe of this novel, none of the rest of the books come to same level of failure as this one does, and if you mostly agree with Clancy's views in the book, it's very easy to gloss over the worst parts.