The Beginning and the Ending
The opening of the movie, and the way it ended are utterly ridiculous in my opinion. I only bring this up because everything in between was actually pretty good. I can't think of any other good movie that had such horrible opening and closing scenes.
The beginning and end have a much bigger effect on a movie than anything else. Ninety percent of the movie was well above average, but since it started out, and ended badly, it just leaves a bad taste.