Chaos Sakura
One of the original first person shooters. I believe it was prequelled only by Wolfenstein ^_^
You would be correct in that belief.
I've, personally, never played he original Wolfenstein, but it was the first FPS (and I think one of the first 3D-based game).
DOOM expanded highly on the principle, expanding sprites and improving quality (I think Wolfenstein was in the 16-bit region, while DOOM was 32-bit (due to the fact it was on the SEGA 32X).) of textures, weapons, pickups, and so forth. Also, I think DOOM improved on the AI of the enemies, too.
DOOM2 expanded on DOOM further by adding a more 3D feel by adding multi-sided sprites (even though DOOM had 3-angled sprites), meaning DOOM2's sprites could be actually facing away from you. It might not seem like much, but it was a huge improvement for the time it was made, I think. I don't think there were any other FPSs around in that time, though I'm sure Duke Nukem emerged sometime during or after the DOOM/DOOM2 era.
