The Tron 2.0 game is great, as I hoped. The gameplay is basic FPS stuff, but the look is phenomenal. Particularly the much hyped glow effect.
A bit of research yielded this NVidia slide deck about the glow effect. It's conceptually simple; render the scene with just the light sources and blur it. Then render the scene normally and add the blur in as glow.
The part that makes this remarkable is they can do this 30 times a second at 1280x960 resolution, thanks to the magic of Cg. Cg allows you to write programs that do things like calculate per-pixel shading to create all sorts of crazy effects in real time. Consumer video cards have an astonishing amount of parallel computing capacity.