A bunch of college guys are in a room playing D&D. The movie switches back and forth between them playing the game, and showing what their characters are doing in the fantasy world. Of course, the same actors play their characters, so you know who's who. But this is a comedy, not some sweeping fantasy, because these guys are playing D&D the way people really play it. That means they crack jokes, they change their minds, their characters do unwise things now and again, and they argue with the DM. And when they do, it affects what we see in the fantasy world.
I ordered my copy today.