How does this book portray dystopia?
A dystopia reflects a dehumanized society living in fear under an oppressive form of government. Very often the government disguises its dictatorial purposes under a cloak of "the people's own good." This would be the case with Brave New World, for example. Other times the government appears openly as a force bent on crushing individuality and individual thought. As a depiction of Stalin's brutal rule, 1984 falls within the latter category.
In 1984, dystopia comes to life through a number of facts that transfer the characters' feelings of anxiety to the reader. We should bear in mind the technological improvements that allow Big Brother to follow the inhabitants of his world day and night, keeping them under constant surveillance, the psychological and physical torture to which dissidents are subjected, the betrayal of loyalty and love that prove to Winston and Julia that they cannot hold on to their idealism and vows when confronted with unbearable pain, and that they prefer life, no matter how debased, to death. Other elements to consider are reporting on "suspicious" behavior, the constant rewrite of the past to suit present developments, and the sadistic artfulness with which O'Brien infiltrates the freethinkers' movement, O'Brien being a stereoptype of a kind of strategy commonly used by totalitarianism in order to better destroy groups and individuals perceived as a threat.
All in all, the novel's portrayal of dystopia is comprehensive, anguishing, and recognizable by anyone who has lived under such regime.