This would have been a five if the ending hadn't disappointed me (though maybe I just didn't "get it"... not enough forums are talking about it yet to find out). But let me say this: if you intend to watch the movie, DO NOT READ ANY SYNOPSES OR REVIEWS. They give away something that would make the movie a lot less awesome to watch.
That being said, this is a pretty brilliant dark and twisted comedy. It's not for everyone because of this, but those that can get over some pretty sick subject matter will definitely appreciate the originality and talent being shown here. Robin Williams gives an awesome performance, and all the other characters act their role perfectly (especially the son, who is incredibly unlikeable).
But I don't want to give away too much here, so if you can deal with disturbing themes, go watch this now.
In a sentence:
Brilliantly unique and well-acted, this movie pushes the limits until the slightly disappointing and predictable ending.