Well it certainly showed a character with some serious struggles, dunno what the real John Nash had to say. I read the book too, long ago, was a different version of events, but don't remember much.
Saw a hard-to-watch movie called "Clean, Shaven" that gets some respect for how it portrays the illness, not sure it's for everyone as it's disturbing at times, looks more realistic. Wonder what some schizophrenics think of that one, but it isn't so famous as Russell Crowe's movie of course.