Brad Pitt and Julia Roberts = 0 Chemistry
The two of them had the least amount of chemistry of any two male-female actors I've ever seen. It was as if they agreed to this movie on the set of Oceans Eleven, thought it would be good, and realized that neither really worked together without George Clooney.
I didn't believe the two of them would actually be together. The movie would have worked slightly better if either one of them was in it, with a different actor in the opposite role.
Because of this, the movie kind of fell onto the story - which sucked. The only good thing about it as is was James Gandolfini.