the best classic fps?

cs 1.6 ofc and half life

Unreal Tournament 99

Perfect Dark

HL, RTCW, QUAKE.

CS 1.6

Definately Doom

Definately Doom

Quake, Doom, Unreal Tournament and my fav, Half-Life. Never played a Wolfenstein, and I don't know why I don't really like "funny" FPS like Serious Sam, Duke Nukem and Postal 2.

Doom

DOOM I/II, by far. 21 year old game that's STILL being modded for. Multiplayer is still quite strong as well. It's one of those games that'll never die.

Medal of Honor: Allied Assault, Golden eye n64, BF Vietnam, i Know BF2142, BF2 are from 2005-2006 but are the best!, Black for PS2, perfect dark, turok 2, CONTRA NES :D and more...

I would say Serious Sam 1st and 2nd Encounter, Unreal Tournament (I prefer the 2003 one, shame it isn't on Steam), and Quake 3 Arena

Doom
Heretic <<< I like this one more
but Doom with Brutal Doom mod is the best shit ever, modern FPS can suck a ****

Doom

quake 1 .. unreal tournament goty

Unreal Tournament (I'd say UT2004, but since you said before 2004 it doesn't qualify :( ) or Quake 2 for multi-player.
No-one Lives Forever 2, Shogo or Hexen II for single-player.

Wolfenstein 3D. One of the best games ever made and to me the best FPS. As classic as it gets.

I still remember the days when I came from the school to visit my mom at work and played it there till closing hours. One of the collegues there was nice enough to show me how to play it. Not the best game for a 7 year old certainly, but damn, it was fun :)

wolfenstein enemy territory/rtcw
quake/doom/duke nukem/UT
soldier of fortune (one of my favourite fps games of all times)

Duke Nukem 3D

Return to Castle Wolfenstein, Hidden & Dangerous 2 close second.