Perhaps you read our recent impressions of Mass Effect. If you did, you'll know that we were mightily impressed with the game's dialogue system. Rather than simply presenting players with a set of scripted responses, Mass Effect more or less has players choose their gut response. This gives conversations a much more natural flow, and as a side effect, actually made us pay attention to what the characters were saying. If a game can actually make you enjoy the things your character says, rather than simply skipping over it, that's a good sign.
Having seemingly read our minds, GameVideos has posted a video of the dialogue system in action. Give it a watch and see how interesting it can be. Take special note of the choices the player didn't make, and you'll have an idea of how many possibilities there are. November can't come fast enough.