Well, I haven't read all the books, but I read several in my youth (because they were around), and they were much, much worse than the movies.
Seems the film-makers largely agreed that it wasn't worth trying to preserve much from the books.
"Diamonds Are Forever" much better than the movie.
In Fleming's "Goldfinger", Goldfinger is actually trying to steal the gold from Fort Knox. It was much more realistic to have him instead trying to destroy the gold to increase scarcity.
Say what you want about the film "Live and Let Die" but reading Fleming trying to write "jive" was just embarrassing.
But it wasn't the plots that I thought were worse, but the writing itself.