GT5

physics are a serious improvement over GT4, with all aspects of the cars handling much more accurately modelled, particularly that of weight transfer and oversteer. Its also now easier are more accurate in regard to throttle control (power over and lift off oversteer are far better modelled.
Now as far as it being overdone, and speaking as someone with a fairly large amount of track and proving ground experience, while GT5

is not perfect (and no sim is) its certainly not as bad as quite a few are making out.
Part of the issue is that we do not even come close to driving these cars in the same way you would in the real world, and we lack almost all of the non-visual feedback we rely on normally. Lets take the Ford GT as an example, it develops peak torque at 4,500rpm and has a fairly flat torque curve, so as a rough figure it will be at around 500ftlbs at 100mph in 2nd. The 2nd gear ratio is 1.71 and the final drive is 3.36 and as torque is multiplied by the gearing we get a torque figure at the wheels of over 2,800 ftlbs of torque or 1,400 ftlbs per rear tyre. Given its static weight dist of 57/43 (rear to front) and that some of that will of course get moved back under acceleration, lets be generous and say its 70/30, with a curb weight of 3454 lbs that's 1,200lbs of load on each rear tyre.
If we assume that these tyres have a fritional co-efficent of 1.0 with the road (which is again being generous), we can see that under straight line acceleration the tyre is already at its limit (1,200ft/lbs of torque on a tyre that can handle 1,208lbs), the moment you turn the wheel and add directional slip into the equation you are going to be over the tyres grip limit (without ever factoring the new load change from side to side that will reduce grip on one of the tyres).
Then add in that we are dealing with a mid-engined car, meaning that any change of direction and therefore loss of control is going to happen quickly and its no wonder that when driving them you need (unless you have one hell of a lot of talent) to accelerate and brake only when you are in a straight line and on long sweeping corners keep your throttle position and steering steady, with any inputs made smoothly.
Now I've posted the following video a few times (as have others), but it does illustrate quite clearly what happens when you don't keep the above in mind and just throw the throttle open while cornering in a low gear...
...and that Ferrari has a lot less torque to deal with than the GT.
Sims and games also have one other problem that exaggerates this, controllers and to a lesser degree wheels and pedals, allow us to go from zero throttle to wide open far more quickly that we would be able to or want to when driving a car in the real world.
Real world road driving bears no resemblance to how we drive in GT5

(or LFS or Enthusia, etc, etc), take a Ford GT out to the Eigar track and keep the throttle at no more than 40% open at any time, keep the revs below 4,000rpm and don't exceed say 70 - 80 mph and you will be in a situation that most 'spirited' road driving will be for a car of this nature. All of a sudden the GT become rather straightforward to drive and its only when we exceed these kind of parameters and step up to and over the limit that it becomes trickier (very much like the real world).
As for why 4wd cars are easier to drive in these situations, well go back to the Ford GT example I gave above and if it were 4wd the torque would be split between four rather than two wheels and as a rough approximation each would have 600 ft/lbs to deal with. Which is well below our 1,208 limit the two rear tyres were getting.
Isn't physics fun.