I saw the movie several years ago. I walked into it not knowing anything about it - I didn't even know who John Nash was. I just finished reading the book by Sylvia Nasar a few days ago.
The movie (directed by Ron Howard) was entertaining, about a mathmatical genius from West Virginia who ends up in Princeton, and does great work, but becomes physcotic. Movies are visual by nature, so it concentrated on the illness & the visual hallucinations, as opposed to other sensory halluncinations. That's only natural. Eventually he began to recover, and the hallucinations never quite went away, but he ignored them. He won a Nobel prize in economics for some work he did before he became ill.
It was a lot harder to read the book than it was to sit through the movie, which I suppose, is the way it should be. I have only very basic math training, and I found it difficult to follow some of the concepts discussed. The book, quite rightly, spent a lot of time discussing Nash's accomplishments before he became ill, and these accomplishment were quite profound. Who knows what would have happened if he'd had those 25 years of illness back. The movie seem to spend more time on the illness - at least what I remember of it.
Some part of the book was spent on the nature of schizophrenia, and if Nash's case was typical or not. Short answer - nobody's sure. He was 30, when the symptoms exploded, which is late for the disease. And he was eventually able to come out of it and control it (mostly by recognizing & ignoring the symptoms), and no one is quite sure if that is something people do or not either.
The book is much more detailed than the movie, both about the math and the illness. It would have been impossible for the movie to have that level of detail and still tell an interesting story.
So, the movie is intertaining. The book I found interesting & very good, but not easy to read. Lot of larger than average pages, each containing a lot of words, and a lot of math.