Animal Farm is a dystopian text because it portrays a world where the characters seek to have a perfect or utopian society, but their plight results in a world that is worse than the world they changed.
It is evident from the beginning of the text that the animals' attempt at a new society based on the principles of Old Major would fail because Orwell refers to their endeavors as a revolution. By definition a revolution is one full (360 degree) turn. This implies that the animals' attempts to better their lives will result in facing the same predicaments and problems they faced initially.
Old Major's ideals about animals working for the betterment of animals rather than the humans, leads to the formation of the idea of Animalism. Unfortunately like most revolutions, the ideals that form the revolution are often distorted to serve the purposes of the individuals leading the revolution. In this case, Napoleon the Pig and his initial ally Snowball, seek for the betterment of the pigs and not all the animals as a whole. Eventually, Napoleon drives Snowball from the farm because he sees Snowball as a threat to his autocratic rule.
The animals on the farm are easily manipulated because of their belief and blind adherence to the principles of Animalism. What begins as a series of commandments
THE SEVEN COMMANDMENTS
1. Whatever goes upon two legs is an enemy.
2. Whatever goes upon four legs, or has wings, is a friend.
3. No animal shall wear clothes.
4. No animal shall sleep in a bed.
5. No animal shall drink alcohol.
6. No animal shall kill any other animal.
7. All animals are equal. (chapter 2)
and mantras "Two legs bad, four legs good!", evolves into a list of rules that are modified to benefit the pigs yet must be adhered to by all animals on the farm; this leads to the animals' downfalls.
Ultimately, the pigs who are lead by Napoleon betray all of the other animals on the farm. This is evidenced by the ultimate betrayal: the slaughter of the loyal horse Boxer. By the end of the text, the commandments are all modified with the last commandment reading, "All animals are equal, but some animals are more equal than others." The pigs reside in the farmhouse, a symbol of the previous human regime, wear clothes, sleep in beds, and drink alcohol. Ultimately, the animals cannot tell the difference between the pigs and the humans who they trade with, as Clover observes through the farmhouse window,
"No question now, what had happened to the faces of the pigs. The creatures outside looked from pig to man, and from man to pig, and from pig to man again; but already it was impossible to say which was which" (Chapter 10, 118).
The animals who could remember life before the revolution know that their life was worse now than before. The other animals did not remember a time without pigs in charge and dogs serving as police and guards.
Ultimately, the animals in Animal Farm seek a perfect society or a utopian society where there would be no classes, no leaders, and supreme happiness. What they get is a world that is worse than they could have imagined, degraded, and headed to its ruin.