Peter Lorre is good as LeChiffre, and Michael Pate as Leiter (or 'Letter' as he's listed in the end credits) is very likable, and perhaps would have made a better choice to play Bond here, but Barry Nelson was mediocre. The low budget both helps the movie and hinders it: it gives it the grittier look that some of the Bond novels have, and also makes it look slightly like a film noir, but also limits it in term of sets and props and lighting (which is often times visible over the actors' heads.) The short run time is also a mixed bag: the film doesn't overstay its welcome, and follows the book fairly closely, (the original novel was so short that it seems almost like a pamphlet, rather than a full length novel) but it doesn't give much opportunity to flesh out the characters at all.
Early TV movie adaptation of 'Casino Royale' has the low key feeling of the original novel.