GeForce 8800 GS is a high-end GFX based on the 65nm variant of the first-shader unified architecture.
It's based on the G92 Core and offers 96 Shader Processing Units, 48 TMUs and 12 ROPs, on a 192-bit memory interface of GDDR3. The central unit runs at 550MHz and the memory clock operates 800MHz. It will consume no more than 105 Watt.
GeForce 8800 GS was added later to the GeForce 8000 Series and was manufactured with an upgraded G8X Core known as G92 (later used on the GeForce 9000 Series). It's manufactured with a smaller technology (65nm VS 90nm) and therefore heats less and consumes less power. Compared to GeForce 8800 GT, it performs significantly worse - especially at higher resolutions.
Today's modern demanding games can be played at medium (most) or high settings (some) smoothly. However, DirectX 11 based games aren't supported and its performance will decrease substantially, as the resolution increases.