After testing the 2.09 physics in my usual GTPElitist™ environment (proper wheel, pedals, no assists, no ABS, track properties set to Real, usage of low-grade tyre compounds, full stock vehicles, etc..), I have to conclude how this update is nothing less then great.
The complete sensation of driving in online is now more believable. Ice Effect™ is almost no more, you can clearly feel the grip-thereshold on the wheel, you can partially recover from high-speed skidding by proper modulation of acceleration/straight-line-braking and my favorite part - braking distances are finally moved towards Realm of Reality™, where you need to start braking very, very, very early on Comfort tyres in order to actually manage to slow down prior to apex.
But my favorite part is this: finally you can drive super-sports cars on Comfort tyres without nasty Ice Effect™ (it was possible before, but not without serious wheelspins and such, which was challenging, but not very realistic). I tested F40, MC4-12C, Enzo and Yellowbird (all cars full stock) on Comfort Soft compound and each and every one of them drives like a charm. Of course, you have to take into account elevations of the corners, track elevations, bumps, kerbs and speed of approach while braking, but feel of driving those beasts on proper compound - without ned to go into semi-slick territory - is great.
I love the new property of more pronounced loss the FFB effect if you lose the grip (red tyres). There is no retain of control, car just goes straight until grip is back. Great.
To conclude, I really appreciate what they've done with this update. Main control now lays in your accelerator pedal where gentle modulations of pressure affects the mechanical grip much more then before. New properties of tyres (where grip levels have definitely been balanced towards more realistic) allows for normal driving of high-powered cars on compound that should be usual if driving them in stock conditions (Comfort). Grip of tyres is more realistic, they absorb lateral and longitudinal movements of the chassis more naturally, resulting with more believable sensation of driving.
I also welcome the new addition of more "loose" model of barycenter which finally allowed the suspension to lift-off the wheels from the ground.
Od course, there are many things that should be improved further (low speed physics would dramatically improve if effects of torque-rev in 1st and 2nd gears would be made less dramatic and more realistic - which would also result with actual standing start getting variable grip more dependable of acceleration modulation, influencing development of grip-property for tyres while cold), but when I look back to times of Prologue and GT5 V1.0 - this is one of the greatest physics update for this game so far IMO.