GT4 physics changed dramatically from GT3. GT3 felt more of a "arcade" driving style, you could create huuge drifts in GT3 with little effort, whereas in GT4 people had problems trying to even hold a small one. the tire properties have changed again in HD, and it's once again easier to get the back end to slide out, but unfort the way the cars steer and handle still feel like GT4, just a bit updated and tweaked for the better. then again it's not like they're touting this as GT5 or anything like that... it's just the HD version and well worth the free download.