I never felt nauseous with earlier FPS'ses and I've been playing FPS since I was 7 or 8 years old and coincidentially, my first FPS was Doom 2 and I never felt that way.
The way older FPS'ses are rendered is very different than how today's FPS'ses are rendered, the older games were 2D based games masked under 3D environments (if that makes any sense). But there are a few games with newer ports and modern engines that makes them less sick indutioning and are much more playable and makes them look much better. Like GZDoom for the Dooms or EDuke32 for Duke Nukem 3D, with those engines, both games are rendered in full 3D and thus, you won't feel sick.
EDIT: Damn, ninja'd... well, my point still stands
