The first 'Half-Life' movie treatment pitched to us climaxed with a tearful reunion between enslaved Vortigaunts and their Vortiwives and children. The last one I saw had Black Mesa invaded by a cavalry unit, just so as to feature a scene of bullsquids tearing into armored horses.

There's a misunderstanding that I've always tried to address straight on when this question comes up, which is that a 'Half-Life' story can somehow exist outside of a game. It can't. The story is created through the process of trying to figure out how to best use the features of the engine within the interesting set of constraints it poses.

The trade-off between speed and image quality is a key constraint of first-person action games, and the job of developing a workable engine involves constantly optimizing both elements. Gamers dream of the day they'll be able to haul their arsenals through three-dimensional environments of photographic clarity, playing 'Myst' with a meat ax.

A game like 'Myst' may be a gorgeous slide show that preserves its beauty at the expense of speed. A game like 'Doom' sacrifices almost everything for action. But the eye soon adjusts: the degree of detail more than adequately conveys infinite claustrophobic labyrinths populated by howling monsters.