I've owned my '06 S4 for 3 months now and I never thought driving a car could be this fun. The AWD, V8, and 4 doors are mostly why I chose it over the BMW M3. The 40/60 torque differential is also a big plus, but note that the S4's w/tiptronic do not have this feature. This car loves gasoline and I average about 17-18mpg overall, but if you can afford this car and you crave performance then gas mileage should not be an issue. The cornering is amazing and the AWD really keeps the car glued to the road. I've even driven on snow covered roads with performance tires and had no drama at all. This car does everything.
V8 that growls, AWD, handling, acceleration, overall performance, first rate build quality, very nice interior, 40/60 torque differential, 4 doors, good ride
Better gas mileage without sacrificing performance, arm rest gets in the way of the hand brake