At least on the 360, there is a distinctive change in the AI behaviour: while once in a while they still pile up in front of corners and have a go occasionally at you, for the better part they try to stay clear of you if they can.
They can put up a good challenge in stock cars and it's quite fun to chase the leader of the pack.
Car handling has also been tweaked dramatically - AWD don't do that sling around thing anymore (ruined the Evo X for me), there's a good measure of super-glue to RWDs (makes the McLaren F1 so much easier to drive, while others have became a bit boring), under-steer vs. snap over-steer in the GT2 Porsche is both less dramatic yet much more fun.
The Supra is superb, interior of the Muscle cars is quite nice, too.
Really sorry you still don't like the game, it can be a lot of fun if one is able to adjust to the general feel.