I don't know about live4speed, but I remember when I played Enthusia for the very first time -- I was amazed at how the game felt like a "Live for Speed
Lite," and that's pretty much how it was in May of 2005. Of course, Live for Speed has moved on since then, and Enthusia is a bit farther behind...
Even today, "Live for Speed
Lite" is about as simple of an explanation as you can get, but I'll try to elaborate.
Most racing games, including GT4, have simple (or not-so-simple) physics engines where everything revolves around the car as a single object. When you turn right, the car rotates to the right, following guidelines about cornering speed and whatnot that were given to it by the programmers. When you hit the gas, the car moves forward, and when you hit the brake, the car slows down, again following guidelines that the programmers set up regarding the limit of traction, wheelspin, etc.
Sounds logical, right? Well, the real world isn't that simple.
Live for Speed and Enthusia both follow the same principle of driving game physics -- they let the tires do all of the work, because that's how it works in real life. In LFS and EPR, the car's visual exterior is suspended at four points by the four wheels, and everything works independently (instead of the car being a single object, the car is five objects). When you turn right, the front wheels rotate to the right, the tires attempt to grip the pavement, and the car responds to this grip appropriately (that's the idea, anyway), instead of just "rotating" to the right. When you hit the gas, the drive wheels (which depend on the drivetrain, of course) are given power, and each individual wheel/tire must struggle for grip on its own, and the push/pull of the wheels/tires are what propels the car, not a simple piece of programming that says "go forward." When you hit the brakes, the car doesn't just "slow down," a braking action is applied to each tire, and each tire must again struggle for grip based on the surface it's rolling over and the weight being placed on it, or the wheel(s) will lock up.
To summarize, GT4's cars were told exactly how to behave by PD's programmers, and can only do what PD told them to do. EPR's cars, and to a much greater extent, LFS's cars, were told by their programmers what each part of the car does, and what the laws of physics are...the cars are free to do (almost) everything that is possible within the laws of physics.
If you have no idea what I'm talking about, maybe
this will help.
The problem with EPR, as compared to LFS, is that compromises were made to make it more accessible -- the steering has a lot of compensation when you're using the DS2. Tires are somewhat grippier than in LFS or real life, especially in the rain, snow, and dirt, and racing slicks are way, way too friendly and predictable in their transitions between grip and no grip. The snap-back oversteer that you get from over-correcting a drift is a bit soft and on the easy-to-control side. The clutch is always slipped in such a way that you get the best launch possible. Locking your brakes is possible, but too easy to avoid...
...you get the idea. Konami tried to make a compromise between realism and playability, and I think they pulled it off very well, producing a game that is both fun
and more realistic than any other PS2 game I've ever played.