One of the more important tests we have in our arsenal is Oblivion. This game really pushes the limits of hardware with beautiful scenery and HDR effects. While the 8800 GTS 320MB owns this benchmark, the 8600 GTS comes in second well above the nearest AMD competitor and the current $200 NVIDIA part it is replacing: the 7950 GT. Even the 8600 GT comes in ahead of most of the pack.
There is certainly an affinity between Oblivion and the GeForce 8 series, and if this is any indication of the type of games on the horizon NVIDIA is in a good place. Unfortunately, we can't know if this will be typical of the future games or not; most likely, it will be true sometimes and not others. It's all really up to the game developers at this point.