Throttle and brake both appear to be linear, or as near as damn it.
Overall the physics are a step up, but I would have to agree with the likes of
@Jordan,
@Famine, and Jimmy that it's more of an iterative improvement than a leap forward.
One thing I do see as a big positive is that you have to now drive road cars to the limit of the car, rather than the limit of the track as you previously had to. Shopping trolly runabouts (looking at you stupid Suzuki Aqua) are out of place on a track and will understeer like lazy dogs if you overcook them.
Still need more time (good job I have the day off work tomorrow), but so far the ITR DC2 feels much better than in GTS, but he diff still doesn't feel aggressive enough, but at least it now feels like it has one.
Not physics-related, but I do have to say, the AI is appalling, and the difficulty levels really don't change that.