Of all the James Bond books, this one feels the most cinematic, though I do wonder whether my knowledge that the novel is based on an idea for a film influences me in feeling this. When two British atomic weapons go missing, M puts everyone on alert, and sends Bond on a mission to the Bahamas to track them down.
Thunderball seems to be different from the earlier books. Bond feels slightly less rough around the edges - he's mellowed perhaps? His over-opinionated ways are much lessened, and he comes across even as slightly vulnerable. The other characters are the opposite. Whereas before there was in depth background about Goldfinger, Rosa Klebb, Dr No and so on, in this book Largo seems to be nothing more than a puppet. Blofeld gets the rich detailed treatment in an early chapter, but is promptly ignored from then on, making Bond's battle with Largo feel rather perfunctory and impersonal.
The detail of the settings is also sparser than before. In earlier books the reader is treated to long descriptions about the different winds, visits to Harlem, casinos, cars and so on, all of which are missing from this book. Instead, the focus seems to be on action and actual investigation - it would be fair to say this is almost the first novel in which Bond has actually had to do some proper spying. It is written as if for the screen and not the page.
I would go as far as to say that the opening is probably my favourite section of the book. This is the part in which Bond is himself and has his usual foibles. It's the part that gives Blofeld such a brilliant background - setting up an ambitious idea on Fleming's part to have an enemy that could feature in several novels.
Overall though I'm afraid I didn't find it to be at the better end of the series, lacking the unique elements that characterise Bond's earlier outings. It's certainly not bad though, just perhaps more in line with a run-of-the-mill thriller.