Long Shots, Not Much Music
One Flew Over the Cuckoo's Nest was released in 1975, and if you watch any other big movie from that time, you'll see that the productive style of One Flew was very popular at the time.
For starters, you're going to see a lot of long scenes where camera angles don't change a whole lot. The overall effect of this technique is to lull you into a sort of trance where you don't realize how quickly time is passing. There are some ninety-minute movies out there that have forty scenes. But One Flew is a whopping 133 minutes and it only has nineteen scenes. Plus, the overall trance created by the long scenes and lack of music mimics the sort of trance-like state that the patients of the mental hospital are constantly in. Fitting, no?
On top of the trance-like state created by the production, there is also a sense of boredom that runs throughout this movie. This boredom is no doubt connected to McMurphy's constant agitation at having to stay confined to the hospital. The eventual effect is one of discomfort, as many people will tell you after having seen this movie.
Some people find the production style boring, others just find it plain unnerving. But in either case, these responses successfully mimic the way you would probably feel if you found yourself cooped up inside a mental hospital.