I think this may be the most underrated James Bond book by Ian Fleming. It literally is a thrilling read. While not his very best, it is a true gem, just with some rough edges.
Tiffany Case is one terrific leading lady by Fleming, one of his better ones, I think. A woman with a strong wall surrounding her for the most part, and one that you do not get to call all the shots with. She goes through quite a change in the story from being the frosty version we meet with Bond's alias of Peter Franks to the much happier one during their nighttime escape and Queen Elizabeth trip.
If there is one problem with this book, it is the obvious one, the villains. Yes, they are hardly some of Fleming's best. Jack and Serrafimo Spang, the beginning and end of the pipeline from England/Africa to the USA, while described as being some of the toughest of the bunch, and made out to be quite the villains, are never given enough actual time in the book to show off exactly what they are. Serrafimo gets a few minimal scenes with Bond, and Jack is....to save for spoilers...hardly in the book much at all. Wint and Kidd are fairly good though. They receive a general amount of time to be shown as a threat to Bond, as odd as they both may be.
The location switching is often claimed as a huge fault of this book, I even used to always harp on that myself, but I've come to see that it really doesn't bother me much at all. London and the USA are done fairly well for me, and I really, really love the moving around in this book. I like reading about the Tiara in the US, and the House of Diamonds, it just feels like a James Bond book.
Very excellent little aspect in this book...
A strong story overall, at times it gets murky, such as in the horse racing, and that sort, but I don't think anything in this story detracts too heavily from the overall plot.
Death is Forever. Diamonds are Forever. And this book is Forever. 4/5