It is a timeless classic. It is a portrayal of Russian historical personalities in the form of animals in a farm. It is about how the revolutions happen but the purpose is short lived as the hunger for power kicks in.
Animals in a farm coming together and rebelling against the dominant farm owner with a purpose to lead an idealistic life of treating all animals equally is the story theme. While they find success in their rebellion, aftermath life of the animals living in peace and harmony is short lived. The purpose is soon lost as one of the leaders of the rebellion, a pig named Napoleon, becomes power hungry and takes control of the farm by force and tactics. He manipulates the commandments all animals agreed to follow to suit his best interests. New order emerges and inequality comes back.
What makes this story interesting is the narration of animal characters resembling human like personalities and how the platform for a rebellion was prepared and purpose is lost. George Orwell has simplified the historical events in Russia to create this story and characters of Animal Farm. But even if we keep this Russia background aside, this book makes a quick and entertaining read. The impact can last for many days, probably a reason for this book to be in print for the last 100 years.