I wasn’t expecting this book to have as much of an impact on me as it did, because it’s so short and I knew most of the plot going in. However, Orwell achieves a memorable, essential read with Animal Farm. It’s impossible to not feel sadness and anger at Boxer’s ultimate fate or at all of Squealer’s lies. Also, that last paragraph with the pigs and humans all looking the same was very well written. 
I did notice that some themes of 1984 appear in Animal Farm, notably with all of Squealer’s twisting of the truth. However, I actually do think this is better executed in Animal Farm than in 1984. Since the book is shorter and is a “fairy-story,” I think it has a greater impact than in 1984, where Orwell hammers this theme throughout the book. While 1984 most certainly is a pessimistic and grim reading of society (which I also recommend), the details can get a bit drawn out. In Animal Farm, the book’s length and simplicity hit on Orwell’s anti-totalitarianism more effectively.
Also, justice for Boxer!!