GameSpot's Doom III Impressions are online, offering extensive thoughts upon seeing what's being demonstrated of DOOM III at E3, saying "we're guessing that id Software's area of the show floor is only going to get more crowded over the course of the show--because word of mouth about how utterly incredible Doom III looks is going to spread, and fast." The article offers moment-by-moment details of what is being shown, all of which was being rendered real-time by the game engine. They describe the intro, weapons, physics, enemies, environmental interactivity, combat, and more. Here is a bit from the beginning offering some impressions of the visuals:

The demo opened with a cutscene showing a planetoid of some sort--perhaps one of the moons of Mars--in the year 2145. The scene changed to show a high-tech cityscape on the surface of the planetoid, and it then panned over to a formidable-looking military installation: the Union Aerospace Corporation. Heavily armed and armored guards stood chatting in front of the facility.

One took his helmet off. The camera moved in to reveal the incredible detail found in Doom III's characters. The characters' facial expressions were quite lifelike as they exchanged dialogue. But what was even more impressive was the subtle detail that could be seen in their individual skin tones and complexions. It's no exaggeration to say that these are easily some of the most realistic-looking 3D real-time-rendered characters ever seen in a game. The quality of the character models--and actually, even the visual design of their high-tech armor--is comparable to what can be seen in last year's computer-animated sci-fi feature film Final Fantasy: The Spirits Within.

Update: GameSpot has even more More Doom III details based on seeing the game at their E3 Sneak Peeks panel, quoting lead designer Tim Willits that "the Doom III technology is completely done, and even though there are still some obvious optimization issues that need to be worked out, the design team is now fully engrossed in finishing the actual game itself." Further, Nine Inch Nails' Trent Reznor and id Software "are currently in negotiations to do the music for the final game," and "id has no current plans to do an Xbox port of Doom III, though the game could hypothetically run on Microsoft's hardware. "