I'm going to assume you mean the cartoon-like version rather than the real-animal version which is not particularly well known.
I always think the book is better than the movie, and Animal Farmi s no exception. One reason is that I form pictures in my mind as I read, and I imagine what each of the characters must look like and where they live as they live out their stories. That's especially true in a novel in which the primary characters are animals. Seeing it come to life in a cartoonish movie was rather difficult, though I did enjoy several characterizations.
That being said, the movie follows the novel fairly closely. Rather than the animals talking, as in the book, a narrator generally tells the story in the movie. Old Major dies while giving a speech in the movie, while much time passes between his speech and his death in the novel. The windmill doesn't blow up and get built again as often in the movie, and any scenes with humans do not quite match with the text. But generally, the movie is accurate.
Two major things set the movie apart from the novel, though. The first is the obviousness of Squealer's duplicity as he persuades the animals that any changes are for their own good. His facial expressions and body language, if you will, are clearly deceitful and conniving. Those things are much more subtle in the text.
Second, the ending of the movie is a major departure from the novel. In both, the animals look through the window and see a "blending" of animals and humans--as if they had become one in the same. The movie depicts this quite well, and then it steps too far. Once the animals see this distortion of animals and humans, they stampede the farmhouse and we are to presume they retake their rightful place as owners of the land. That is a significant departure from the novel--and from history, frankly. We want them to assume power, but they don't.
The movie is fun to watch for 30 minutes; however, it is not a completely accurate depiction of Orwell's novel.