If you made a movie about the abuses of a meat packing industry and your audience was the owners of several meat packing firms, you wouldn't get good reviews. That mostly explains the unusually low score for this movie. Its not likely to bring glee to the eyes of those that usually adorn the walls of the local multiplex.
The film is pretty good satire. Its satire not only comes from the situation, but the foreboding mood that lurks throughout the film. It takes on multiple dysfunctions in American life. These would include corporations, Oprah Winfrey, Junk Food, Televangelists, Suburban Households, Materialism, etc.
The film does this all pretty well. There are some occasional flat notes; this would include Zach Galifianakis going into overly long star offs. Most of the staring he does is within bounds, but sometimes he crosses the line. Some of the satire was lacking any subtlety; I'm thinking of the life coach who tries to cure Zach.
Many people have compared this to Brazil, its a fair comparison. In terms of quality, this movie is light years away from Brazil; that is very important however. The one plot point that greatly diverges with Brazil is the ending. I liked the ending to this and thought it fit very well with the rest of the movie. If it ended another way, the film may have come off to much as a wet rag.