Yesterday, I recibed mine. First impressions: Prologue is a different game! Without driver assist, control traction and normal tires, it is very challenging, and also it depends A LOT on the type of car you drive (that shows how realistic is handling in GT4P).
I let my wife try it, she's very new to this kind of games (she loves RTS games), so I switched on driver assists, control traction and arcade tires. After a few laps, she was starting to learn (she drives in RL too), and when it was my turn, I forgot to go back to the simulation setting, and what a surprise! It is very, very, very funny, very arcade, but also "real" in a weird way...
I am still learning and waiting for a free afternoon to get a good training with the wheel and the racing seat, but with this wheel, GT4 will be an amazing experience, even if you go for a quick, arcade race.
One last thing, like in RL, when you lose your car, it is very challenging (because of the 900 degrees of turn) to "recover it", almost scary!