I have played the preiview verison (GT Prologue). It was at Tokyo Auto Salon and at Tsukuba Circuit during a semi pro race weekend.
Prologue is the like the Arcade selection of GT3. A fixed set of cars and tracks.

The game's physics and AI are very similar to GT3. For the road racing crowd, who may want more real world w2w action, GT4 Prologue seems much like GT3. It did seem like the other cars were more agressive in trying to pass and defend. Then again it is the arcade version with the rubber band affect.

I only played the game once. The new wheel is a big improvement over the previous wheel.

My opinion (being a former w2w racer) I think it will make a good game to buy. The ricer-boy in me will enjoy the game.

Greg, Living in Tokyo.