The reason you find FC very oversteery after playing a lot of GT4 or GT5P, is the mirror-image of the reason I find GT5P unpleasantly understeery after playing a lot of FC. The cars in FC are very prone to snap-oversteer - it's one of the things that makes it challenging & interesting IMO.
I wasn't going to say anything, but after a few people were given a pillow fight, I thought I'd add a few pennies.
First of all, Biggles quote. No, it's not that I'm used to GT4 and Prologue's understeery physics, which after a little run in the Supra, I'm beginning to think aren't so unrealistic after all. It's the fact that the Ferraris are all oversteery. Not just snap-oversteer, but oversteer period. You have to apply some throttle in order to keep the car aligned properly through turns, or the rear end wants to swing out. This is due to the mid-engined design, and the physics might be exaggerated but I'm assuming it's pretty close. But oversteer is incessant. I have to watch the cars VERY carefully through the turns because that nose just wants to keep going. And unfortunately, I have to watch EVERY turn very carefully because the driver views are all pretty lame for me. It's like Eutechnyx drew a line through the driver's head level to a point 500 feet in front of the car, and said, "The driver cam will be on this line." Since I can't stand bumper cam, or a cockpit cam that as usual is like driving from the rear seat, that leaves chase cam, and it's WAY too low. I can't see the road for squat so I end up guessing through every turn. But what choice do I have if I want to play? And of course, that means when the car wants to keep turning, I usually don't know it until the nose is pretty far into it, and then I have to jerk the wheel, just like Forza, to get it out of it. And in the rain, that's a very bad idea.
Which brings me to my second point. This is basically the Forza 2 engine juiced up with PhysX. This isn't a bad thing, as Forza is a pretty good game. But because of the issues with their physics engine, like the tendency to oversteer in every car, taking a turn at competitive speed isn't as natural as in other games. You need to have a driver view which connects you to the car well, or these issues will bite you because the feel of the car in Forza 2 isn't quite natural. If you're all about bumper cam or lean back cockpit cam, then FC will probably be awesome for you. If not, the driver cams are worse than they are in Forza 2, or most games for that matter, so the issues will bite you a lot more.
And why do I harp on driver views so much? I had a friend who I turned loose on Forza 2 back when I was still fairly enthusiastic about it with my cheapy but useful MS FFB Wheel. It wasn't pretty. He struggled with everything in a Miata, which he owned and used to autocross with. He still insists it's one of the coolest cars you can own, but whatever.
But in Forza 2, he couldn't get dialed in and it was really bugging him. I told him to hold on, put the Forza rig away and set up the DF Pro and GT4. Set him up with one of my untuned Miatas, and his eyes opened. "Hey, this is more like it!" he enthused. "This feels a lot like my Miata." And it seems the key was a combo of physics which were a little more natural, and roofcam.
I bought GTR Evo, the first PC game I bought in ages since getting the DF Pro. I tried GTR1 and LFS first years ago, but had issues getting the DF Pro wheel to work right with them, and I found out to my horror recently that the PC tried to eat it, and finally succeeded. The driver views in GTR were bad. Driving a high performance Saleen was a chore. I hated it. I felt completely disconnected, despite the FFB. I constantly messed up turns or hit other cars. With Live For Speed, the wheel was getting wonky so I switched to a controller, which gave me a very bad taste of the feel of the cars, but from the physics they seemed very good. Driver views though, once again, very bad, and with a hand controller, I just ended up roasting the tires, so I resigned myself to throwing the cars around to test the physics, which did seem amazingly lifelike. But racing? We'll have to see. I'm probably going to save up for a dedicated PC racing wheel so I'm not endangering my DFGT wheel.
Back to GTR Evo. Wow, I can actually drive the cars as if I was driving a car. I can take turns with authority, mess up when I'm pushing the car too much rather than because I'm fishing for the proper line and speed. I can follow cars closely, and usually hit them when they slam on the brakes. Why? They give me driver views which work. And I can even adjust them to tailor them even more to what I prefer. And by golly, no roof cam! There is one in the replay controls, and I'd love to be able to hack that into the driver views, but I'm not handicapped because the rest of the views are irritating. It's darn fun. It's not more of a chore or struggle than it needs to be.
Which is where I am with FC. It's not the physics itself. I've driven Forza 2 pretty solid for 11 months, so I'm used to it, and even IT'S yucky driver views. But combine pretty different physics with driver views which just won't put me in the car, and it can be hell. Fighting the track and the other drivers is one thing, but struggling with everything is another matter entirely. If the developer can't put me in the car, it's not my fault, especially when it works so much better for me in other games. And I suspect that's the problem with everyone who doesn't like Ferrari Challenge. I'll keep my copy, but it's going to be a while, a long while, before I go back to it, when I have a few days to just blow, because that's what it might take to ace a handful of races.
My rant for the day.