All 3 are very very important!
Shadows with the AA need to be fixed! The jagged shadows on your dash, and on the cars bumper in front of you, and the grid look dirt is just appalling and should not happen! When there are times when the shadows are smooth in the cockpit and backseats etc should be the case all the time!
Sound is a big must! Cars still sound all the same! What ever happen to individual sounding cars? Cause hang on, all cars have their own unique sound right? or am i missing something? And the tyres screeching, like c'mon, for a next gen console/game you would think this would be greatly improved! but it is still the same as the very first gt on ps1!
I've played games on the ps1/sega saturn that have tyres sounding better then that! lol
And well physics, it speaks for itself, of course its a very important thing, Would be nice to have a stall effect too! But overall the physics are half decent in gt5

obviously it will be a lot better then what it is now don't forget prologue is only a demo, full versions of games always pack more punch. Just hope the issues I've stated are something that is addressed seriously and accordingly