Grand Theft Auto IV's physics haven't received much attention, but it's one of the first major titles to use the new Euphoria behavioral physics system. It was heavily touted in previews for Star Wars: The Force Unleashed, and will also power the dynamic tackles in the upcoming football game, BackBreaker. To get a quick idea of how fun the new physics can be, have a look at the following video.

Notice the hysterical caption at the top says that you can press Y to dive out of a moving car, so the player immediately tries it.