The Last Supper is a classic example of an underachiever. A movie with a fascinating premise that falls well short of what it could have been. A general, all-around disappointment.
The film is about a group of lefty graduate students in the Midwest who hold weekly Sunday dinners at their house, each week inviting a different guest for conversation and debate. After accidentally killing a surprisingly obnoxious and threatening guest, the group decides to intentionally invite people with whom they disagree politically and try to change their minds throughout the course of the meal. If they can't, they those people will be killed, for the betterment of the world. The group then proceeds to get increasingly psychotic as they dine with and then murder right-wingers of various natures (homophobic preacher, male chauvinist, book burner).
This premise invites all sorts of interesting questions--how far is it morally justifiable to go in the service of your beliefs? Is the world really better off with some people not in it? As the movie's characters keep putting it, if you found yourself having a drink with Hitler in 1909, before he'd done anything wrong, would you kill him? Unfortunately, rather than actually attempting to explore any of these things, the film instead presents five of the most irritating, self-righteous liberals possible, most of whom are badly acted and all of whom suffer very bad dialogue. They are no less dogmatic than the right-wingers, and they have the added advantage of knowing which decanter the poison is in.
Basically, the film takes an interesting premise and mixes it with bad writing and bad acting, coming up with an end product that isn't really worth watching.