There's extra stability control, self steer assists, and drift assists (which are need for the drifting, but not for proper racing).
You might have noticed the cars don't like to accelerate while turning, that's the extra stability control, and if you start to get sideways, the car tends to 4 wheel slide, that's the drift assist. The self steering is a little more subtle, it kinda smooths out the players input, making the cars less responsive but easier to drive, its really noticeable in the drift vid that its no longer there, as the car becomes really twitchy.
As I said, the biggest difference was the touch of toe in on the rear, if all codemasters did was patch that into the game, everybody would love it so much more.