This is a classic that I just saw for the first time. It's a political thriller with an amazing cast -- Frank Sinatra, Angela Lansbury, Laurence Harvey, and Janet Leigh. They're all great. Angela Lansbury, in particular, gives a performance I will never forget, as a super-evil power behind the throne.
The movie was made during the Cold War, and it portrays Communist Russia and China as the epitome of evil. At the same time, the movie also takes swipes at Joseph McCarthy by portraying a character, clearly based on McCarthy, as a buffoon.
The plot involves brainwashing, which is shown using very creative filmmaking techniques. I won't say more so as not to give anything away. There is a lot of suspense, especially at the end.
The DVD that I watched had three extras: the original trailer; a commentary track by the director; and a short session filmed in 1988 where the director, the writer, and Frank Sinatra looked back at the making of the film -- at times wistfully. It seems like making the film was a highlight in the lives of all of them.
There are also other DVD editions that have additional extras.
The only negative thing I can say is that I was confused by what happened in the very beginning before the credits, and so I watched that part twice. I'm glad I did, because what happens then is important to understanding the rest of the film.
I haven't seen the remake, so I can't compare the two. But if you haven't seen this one, I recommend it!