This is typical of Orwell's style and content. It is forceful, direct, and metaphorical, removing any idealism about the future or rebellion. Orwell often writes plain, readable text that explains ghastly ideas with very few words—this is a great example.
The quote reflects Orwell's main warning in 1984: the danger of dehumanizing, uncontrolled political power. Here, Orwell paints a world where violence is not a tool, but a byproduct—the state only exists to ensure its dominance, and even freedom or the potential for truth is eliminated. This is a common theme throughout Orwell's work.
Orwell uses imagery ("a boot stamping on a human face") to create a reaction from the reader. His austere structure maximizes the effect of his thoughts, there being no extra space, only a tough, unadorned truth. His symbolism is there too: the "boot" represents the overwhelming grasp of the state, and the "face" represents the trampled-on identity of the individual.
This is one of the most heavy sentences in 20th-century fiction, and shows Orwell's ability to use brief, concise language to attack political systems and probe the blackest possibilities of human society.