Interestingly, a lot of that realistic atmosphere came from them shooting on location in a real mental hospital in Oregon.
The performances of what's basically an ensemble cast are uniformly outstanding.
I didn't really care for Cuckoo's Nest when I saw it first, mostly because I have an aversion to Jack Nicholson, but I have to admit that watching it now, so many years later, I was really impressed with him and with the rest of the movie. It truly is a must-see.
And Warners has done it justice with this 4K disc. Alas, there's no Blu-ray included, but the 4K disc looks and sounds terrific, and includes some really worthwhile extras.
The film was apparently restored for its 50th anniversary, supposedly from a new 4K scan of the original 35 millimetre negative, with extra tech used to make it even better. And it works. The film looks exquisite! The image is very film-like, with fabulous detail, a nice but not overpowering dose of filmic grain, excellent colour and lovely blacks. It's easily the best version on video yet.
The audio isn't quite that good, but for a fifty year old soundtrack it's still impressive. The default track features a DTS-HD Master Audio version remix and they did a nice job of it. There isn't a lot of surround, but that's fine because the original soundtrack wasn't in surround at all.
Then there are the extras. You get two short documentaries that are basically Zoom sessions with producer Michael Douglas and actors DeVito, Lloyd and Dourif. Both are quite interesting as these veterans reminisce about an important time in their lives and how proud they are of the film itself.
Then there's "Completely Cuckoo", a really interesting, though ancient (no widescreen or HD) hour and a half documentary that features just about everyone connected with the film, as well as one name not connected to the film (which the filmmakers admit to have regretted): Ken Kesey, author of the original novel. It's an excellent look at the gestation and reaction to the film.
There are also a few deleted scenes.
Very highly recommended, much to my chagrin for dumping on the film in years past.