John Nash (Russell Crowe) was a dweeb. A stereotypical math nerd with no social skills. Unlikeable and unliking. On the other hand, he was brilliant and devised a mathematic schema that became the cornerstone of modern economics (or something like that) and won the Nobel prize.
Like many math nerds, his behavior and mannerisms seemed strange to those around him, and he often seemed lost in a cloud, even to his wife (Jennifer Connelly). It takes a while for everyone to figure out just why.
The first time I saw this movie, I thought it was the most tedious, disjointed film I'd ever seen. Now that I've watched it again, I did find it interesting. I wouldn't put it in my top 100, but I do find Crowe and Connelly to be particularly affecting. Ed Harris as Parcher made the creepy pendulum swing from friendly and protective to menacing quite easily. I'm not sure if the "big reveal" is that much of a reveal any more, but I won't spoil it for anyone else.