I must disagree with many of the film's critics who found this to be a pleasant and amusing view of a complicated family holiday reunion. Perhaps because of my background as a mental health professional, I found this to be a very confusing and inconsistent attempt to picture what could have been a funny family event. The writers touched so many bases that one wonders if five families could have contained the many quirks, pathologies and eccentricities found in this single unit. My overall impression was of the incredible nastiness this family displayed toward the fiancée of the eldest son, a person no one but the youngest daughter had ever met, but who became the target of hostility, primarily based on the report given by the nasty little sister. The fact that the parents were incapable of maintaining even a modicum of civility or to set the example for the children, speaks to their dysfunction rather than the humor of the situation. Yes, I realize that a terminal illness was also an issue, and yes, Keaton is a fine actress, but her character failed the test of grace--more the writer's fault than Keaton's.
I think that what would actually have happened in this situation is that either the eldest son would have upbraided his family for their boorish and cruel behavior, taken his fiancée and left(if he was really committed)telling them they could call him when they grew up; or, the fiancée, seeing that he was not really committed, would have left, herself. However, had either of these things happened, the movie would have been about 20 minutes long, too short for Roger Ebert to have waxed eloquent.