Casino Royale is the first James Bond, written by Fleming over a period of two months in his favourite hideout in Jamaica. It is primarily inspired by Fleming's personal experience in the diplomatic circles -- and I would say this is what distinguishes this from other spy-novels.
It is a beautifully written book. The plot is nothing extraordinary, but the writing elevates the book to the great spy novel level, worthy of the name of Bond. Already in the beginning I enjoyed Bond's description: