Cube Environment Mapping
This is a real nice feature, and it should improve game experience by a good amount. Cube environment mapping is a technique developed by SGI a while ago and NVIDIA will be the first to bring it to home desktops. The idea is pretty simple. From an object with a reflective surface (and not from the room center, as I read somewhere else) you render six environment maps in each room direction (front, back, up, down, left, right) and use those to display the reflections on this object. It can either be used to reflect in detail or blurred, but it can also be used for more accurate (per-pixel) specular lighting. The viewer/camera can move around the reflecting object without you noticing distortions or other artifacts in the reflection, something that's not possible with sphere environment mapping. Cube environment mapping is fully implemented into DirectX 7 and will certainly be found in 3D-games very soon.
GeForce will also introduce 'vertex blending', which basically joins different pieces of geometry with each other, as e.g. required in joints of characters or animals. 'Particle Systems' is another DirectX 7 feature included into GeForce, and NVIDIA has a rather impressive demo for it. Particle systems could be very useful to render nice explosions (what's nice about an explosion?) or the fountain in Billy Christal's garden from 'Analyze This'.
Let me not forget to list the 350 MHz RAMDAC that should be good for the best CRTs and the fact that GeForce is currently still manufactured in .22µ process.