Well, obviously if you watch any film with certain preconceived expectations, you often tend to be disappointed. This film cannot be taken at face value.
First of all, the film was never about the main protagonist visiting her father. That's just background. The film is a construct, designed to take the Mickey out of detective films and show just how absurd they can be. I'm a murder mystery lover, so I can totally sync with this extraordinary piece of fiction.
Of course the characters are deliberately presented as shallow - it was never about them. The plot is designed to be confusing - mimicking that of so many wannabe police thrillers. The music cleverly loops in and out of comedy-horror moments, and the foreshadowing is made fundamentally clear, almost as soon as Sarah walks into the house carrying the food. The flashbacks are, again a parody of what you see in films that want to be taken seriously.
As the plot progresses, the film delves into the ever-increasing circles of now-way-can-this-happen actions: exactly as in so many ridiculous murder films there's a killing spree, and you wonder if anyone's going to be left alive at the end.
It's a brilliant psycho analysis of everything that can and does go wrong in ambitious but rottenly written detective films, and consequently a joy to watch. Just bear in mind that you cannot take this film seriously. If you don't you'll be fine.
