If you're looking for a simple and common shoot'em up and blow'em up war movie, then this won't be a good choice for you.
This movie has a complex plot, and it focuses on that other than simple guns and shooting and killing that so many war movies focus on. There is an intricate spy story in this movie, and those who wish for simple action will miss the compelling plot that Alistar Maclean wrote specifically for this movie. (He wrote the screenplay before he wrote the actual novel).
Richard Burton was an excellent choice as the British spy, and his sidekick Clint Eastwood was another fine choice. They both play their parts very well. Some may say that Richard Burton is 'over the top' in this movie, well, you are correct. But Richard Burton ALWAYS plays his parts like that. Anybody who knows the work of the screen legend would not accept otherwise.
Do not listen to the naysayers here. This is an excellent movie that gets right into the thick of things very quickly. There is no annoying sub-plot. Everything may seem overwhelming at first glance, but there's a reason behind everything done and said. As I said prior - pay attention, you are watching one of the best war/action/adventure movies ever made.
Pay attention when you watch this one.