Wow, talk about late to the party. I got my gt4 last night, thought I'd post some new info. Looks like its already been done.
Anyways, responding to ZROC, Laguna Seca looks entirely different from gt3, mainly because its daytime, not sunset. Obviously its the same track, but with different lighting and different physics, it feels entirely different I think.
As for other tracks, they've been polished up a bit, but are pretty much the same I think. One part of Deep Forest felt like they may have changed the elavation at one part, but I'm not sure. Haven't had a chance to check out all the courses yet.
I'm sure people have posted about the handling before, but there are a few things I've noticed. First, the nose of the car REALLY dips down sometimes when you brake. Second, when you turn, after to let go of the pad, the wheels straighten out immediately. In gt3, it felt like there was a split second after you let go during which the front wheels slowly returned to straight. It makes the car look a bit jerky in replays, until you get used to it.
Great game, I'm have fun. There are 16 B license tests. I've golded 15 of them, and got two prize cars, so I'm guessing you get 1 prize car for all bronze, another for all silver, and another for all gold. (I was literaly .001 away from gold on the 16th test. That occurance hasn't changed.) They`ve got coffee breaks too. One is an open area with cones spread out randomly in front of you. You`ve got to get to the other side off all the cones without hitting any.