NVIDIA have put lots of effort in to the 8800 to try and ensure that ATI has no arguments going for it anymore. Specifically, this boils down to the ability to render full HDR as well Anti Aliasing at the same time. This only applies to two games currently (Oblivion and Far Cry) however it was still something NVIDIA needed to address. With the 8800 series, NVIDIA have added full 128 bit precision which allows for proper HDR to be rendered along with AA filtering.
Along with support for AA and HDR, the 8800 series also comes packing new AA filter tech. It's called Coverage Sampling AntiAliasing and is designed to provide high levels of AA at a minimal performance loss. This is cut from NVIDIA's press package: New CSAA modes include 8x, 16x, and 16xQ. Each of these CSAA modes enhances built-in application antialiasing modes with much higher quality antialiasing. The fourth new mode, 8xQ, is standard 8x multisampling.
Here's the standard image they package with the card to show the difference:
Also new in the image quality category is NVIDIA's promise that their AF algorithm in the G80 does not take shortcuts. They are claiming that there are no optimizations being made and we're hoping that this turns out to be true in the course of things.