GameSpy have coverage of a public interview with John Carmack which covers Doom III and game design in general:
"Of course, it all started with DOOM 3. The lights dimmed and once more crowds were awed with footage. Whereas last year we got a taste of what's to come, this year we got a gulp. DOOM 3's darkened, flickering corridors were now populated with 36 flavors of horror. Along with zombies, we had zombies with chainsaws. Strange spidery creatures with bony limbs scurried in and out of the shadows. Imps clambered down pillars, moving not unlike Gollum from Lord of the Rings. Monstrous demons hurled around smaller zombies like throw pillows. There were creatures that resembled baby-heads with moth wings. (!) Room after room was filled with cinematic 'scare' moments, such as when the half-human figure submerged in a tube of bubbling fluid suddenly jerked itself against the glass and screamed."