Absolutely compelling. The story itself was really interesting - a war/military-themed thriller, with murder, manipulation, hypnosis, incest?, assassinations, martial arts, lots of cigarettes, and evil Angela Lansbury. Could anyone ask for more?
Well, thankfully the acting, directing, editing and cinematography is fantastic as well. The dream sequence is possibly one of the best conceptial and well-edited pieces of cinema I've seen - it tells the story with few words yet leaves a great impact.
I undertstand why this movie was not available for many years after the assassination of JFK, but if you can get your hands on a copy now I would highly recommend it.