Ebert, Roger (1975). One Flew Over the Cuckoo's Nest. Retrieved April 11, 2008, from rogerebert.com Web site: http://rogerebert.suntimes.com/apps/pbcs.dll/article?AID=/19750101/REVIEWS/501010348/1023

In his 1975 film review of One Flew Over the Cuckoo's Nest, Roger Ebert lauds the film for possessing stretches of brilliance, but states that the factor which keeps the movie from being great is director Forman's insistence on trying to assign to it a broader philosophical meaning. According to Ebert, the film attempts to be more significant than its story will allow. For example, in the scene in which Billy is discovered sharing a bed with one of the women McMurphy brought to the ward, Billy talks back to Nurse Ratched, his usual stutter conspicuously missing from his voice. The intention of this message is clear: it is devised to show that Billy has been liberated to some degree by both McMurphy and his nighttime experience. However, it lacks subtlety, and takes away from the film's generally thoughtful and three-dimensional characterizations. In fact, according to Ebert, it is these characterizations that constitute the best aspects of the film. Ebert believes that Forman should have focused his efforts on examining the characters and using their interactions to develop the film, rather than trying to create an antiestablishment parable.
I agree with the review on many of its key points. The movie's strongest facet is its ability to develop its characters and portray them in a way that demonstrates their change and growth throughout the story. McMurphy's significance as a character does not lie in his crusade against the establishment; rather, it is his ability as an individual to change the patients around him, and, by interacting with them in his carefree, individualistic manner, to release them of their inhibitions. It is also interesting how each character responds differently to McMurphy based on their personality. Cheswick, easily influenced, immediately takes to him, while Harding, who is naturally suspicious and guarded, never warms up to him. The nervous Billy is cautious but open, while the wild Taber does not seem to care about McMurphy's presence at all.

Bialostocki, J. (1981).Forman's Cuckoo's Nest, its composition and symbolism. Artibus et Historiae. 2, 159-162.

In “Composition and Symbolism,” Jan Bialostocki describes the technique and imagery that Forman uses in One Flew Over the Cuckoo's Nest to comment on the social dynamics of groups, and the constant struggle of individual expression versus normative stability.  The article begins by invoking the imagery in Cuckoo's Nest's opening and closing sequences.  The vast landscape that the mental hospital in the film resides in plays an important symbolic role—in the beginning of the film, it is a visual representation of the isolation and confinement of the inmates, while at the end of the film, the image of the Chief running into the distance of the landscape signifies the escape from such a closed world.  Bialostocki also asserts that the isolated psychiatric ward is a metaphor for the human world in general.  Within the confines of this environment, we can observe the facets and problems of human nature, such as the dependence of the inmates on one another and their need to participate in community life.  McMurphy, as a rogue figure, acts as a catalyst for this human nature.  Before his arrival, the inmates are meek and mellowed by the drugs they are taking, and the strictly regulated system they are forced to abide by.  Once he arrives, however, he liberates them from this rigidity, allowing them to release their inhibitions and inciting in them real, human emotions and reactions.  Although freeing, this also introduces conflict to their previously uncomplicated existence.  By pursuing their individual needs and impulses, they in turn sacrifice the order and comfort of the community.  McMurphy's individuality walks the thin line between freedom and anarchy, and eventually results in a tragic finish.  In the end, McMurphy is defeated by the system which beats down dissent, and treats individuals as though they cannot make their own decisions.  Only the Chief is affected and liberated by McMurphy's actions as he makes his escape.  The other inmates return to their formerly grey lives.  Having seen the destruction that human emotion and freedom can bring about, they revert back to the passionless, vegetative comfort of their old system of norms, thus letting go of the of innovation and expression they enjoyed for that short period of time. 
This article is interesting because it brings to light the meaning and symbolism behind this story.  It is not merely a critique of the institution-based mental health system, but a commentary on human society in general.  According to the article, illuminates the problems inherent in society, and the difficult trade-off between group safety and security and individual expression.