We had a chance to visit with Valve Software at E3 2005 to see The Lost Coast, an all-new level that Valve describes as "a tech demo that shows off HDR lighting." The visual effect served two different purposes in the demo: first, as an alternative to bump-mapping by rendering a bumpy stonework wall (which was actually flat and not textured in the least), and second, to realistically model the way players will perceive light and shadows.
The level took place on a wide-open, ascending path leading from a dock up along the side of a mountain, with alternating hallways and parapets. While the sunlight on the water shimmered as prettily as it ever did in Half-Life 2, a more-notable feature was the way the new level accounted for changing light conditions. Since much of the level was spent climbing up the mountain toward the sun, at several points we found ourselves looking into the sunlight, then being temporarily blinded as we stepped into shadow. The Lost Coast's HDR rendering will apparently model the action of healthy human irises by contracting (and shrinking) your field of vision in extremely bright light, then slowly expanding in shadows. The overall effect was a subtle but realistic readjustment each time we stepped in out of the sun; any architecture or enemies appeared as indistinct blobs for a moment before our "eyes" would have time to readjust and refocus on our surroundings.
The Lost Coast will be as much about the technology behind it as anything else, though from what we've seen, the level will also have at least a few hostile Combine soldiers hiding in nooks and crannies along the face of the mountain. (And after you dispose of them, their corpses will slither down steps or tumble off precipices as you'd expect.) The level itself will apparently be available later this summer as a free download on Valve's online delivery service, Steam, for anyone who has purchased Half-Life 2. However, Valve remained silent on any details pertaining to Aftermath, the upcoming expansion pack to last year's award-winning game.