is a very nice article about the paper.
The Nash equilibrium is useful not just when it is itself an accurate predictor of how people will behave in a game but also when it is not, because then it identifies situations in which there is a tension between individual incentives and other motivations. A class of problems that have received a good deal of study from this point of view is the family of “social dilemmas,” in which there is a socially desirable action that is not a Nash equilibrium. Indeed, one of the first responses to Nash's definition of equilibrium gave rise to one of the best known models in the social sciences, the Prisoners' Dilemma.
It's just an experience to read a Nobel-worthy piece of work in a few minutes.