Emotional therapy hasn’t been this action-packed since The Sopranos. If this crackling action comedy, about a pair of married assassins (Angelina Jolie and Brad Pitt) who are both unaware of the other’s lethal profession, falters at all, it is by overworking its underlying theme of marital strife. The similar The Incredibles was far more effortless, but at its best Mr. and Mrs. Smith envisions relationships the way they feel: as if they are a matter of life and death.