For clarification this is not the Daniel Craig James Bond movie from 2006. It is the 1967 version staring David Niven as James Bond. Also it is a parody or spoof movie instead of a typical James Bond spy movie. There are two memorable things about it. Firstly it has an awesome cast that can be described as some of the best and most acclaimed people in the industry back then and secondly it had countless troubles during production that harmed this movie (Don't know if the term development hell existed back then). The story is set long after the retirement of James Bond. Because of a new treat by SMERSH the MI6 tries to get him back into action (SMERSH is not transferred in the movies. In the books it is a dangerous Soviet intelligence agency that even James Bond has troubles dealing with and is itself based on a short lived real Soviet agency). Like I already mentioned it is a parody of James Bond and all tropes, stereotypes and hallmarks. Sadly while the movie has some really good and clever ideas most jokes did not work well. When I first watch the movie it looked uneven for me like many parts not fitting well together. Later I discovered that this was even a correct observation. There were 6 different directors participating in this movie on top of rewrites and conflicts or better said problems on the set. The budget exploded from 6 to 12 million dollar which made it the most expensive James Bond movie back then (If I remember correctly). These problems ruined the movie. I think it could have worked if done with a better script and one director. Just look at the cast. It is not short of being a dreamteam with David Niven, Peter Sellers, Woody Allen, Orson Welles (Yes that one), Deborah Kerr, William Holden, Jean Paul Belmondo and more. It is a list of excellent, well acclaimed and successful stars. Maybe this is also a reason this movie failed. There were some stories of animosities between the stars. Overall this movie is a mess and while it has its moments it is still below average. It remains a bit of obscure James Bond knowledge. Bonus knowledge: There is even another Casino Royale movie from 1954. It was a TV movie and is almost forgotten and not many have seen it. Ian Fleming sold it to boost the James Bond recognition and brand but ultimately regretted it latter on.
Unfortunately, after the introductory sequences, Casino Royale begins a downhill slide. It gets progressively sillier and more incoherent until it's impossible to keep any of the plot elements straight.