My annoyance had to do with what felt like a breach of contract with the audience at the very end. The story involves a good family man who finds himself struggling with a (paranoiac?) sense that all is not right with the family that moves into the quiet suburban neighborhood in which he lives. His suspicions grow as the story progresses, and are finally proved to be not without foundation. He uncovers their plot to bomb a large office building in the nation's capital, and the last scenes depict his desperate efforts to stop them before it is too late...
He fails. The plotters succeed in destroying not only the building they have targeted, but also our hero's life, his reputation, even his innocent family.
My problem has to do with the mythic structure of the movie. When you have good guys and bad guys in your story, no matter the intervening frustrations and set-backs, the good guy needs to win. Okay, I know this is not what always happens in "real life." Too often, perhaps, the outcome is at best ambivalent, at worst contrary to what common morality and decency would hope for. But the structure of a movie is a mythic pattern which implies a tacit agreement with the audience that the social order, upset at the beginning of the story, will be restored at the end. The state of Denmark, no matter how rotten at the start, will be restored to health even if, as in the case of classical tragedy, it requires the sacrifice of the hero's life.
In this film, though, the terrorists not only managed to destroy their target, they walked away free to perpetrate another outrage on another day. This offends not my understanding of the realities in which we live--I would be foolishly naive to ignore the fact that there are terrorists at large in the world, many of them ready to attack at any time--but rather my sense of what I bargained for at the beginning of the film. I feel cheated, tricked into establishing a certain set of expectations, and violated by the eventual outcome.
The contract of true tragedy is a social one: the hero/king dies in order that his subjects may be spared the karmic consequences of his individual hubris. (My Buddhist sensibilities also are offended!) The ending of this movie is not tragic, but pathetic. Our hero dies, and his death leaves only a greater threat to the social order he had tried so hard, and with such bravery, to protect. True to "life," maybe. But not to the mythic pattern that would leave an audience satisfied. Or, in Jon Stewart's formulation, restored to sanity.