There are many worthy games.

Halo: CE
Half-Life 2
Doom
Goldeneye 007
Bioshock

Counterstrike: Condition Zero
Counterstrike: 1.6
Counterstrike: Source
Call of Duty 4
Goldeneye 64

counter strike
medal of honor heroes 2
far cry
goldeneye
turok 2

1: Half-Life 2: Episode 2

2: Half-Life 2

3: Deus Ex

4: Call of Duty (the original, none of the others are even close imo)

5: Unreal Tournament (again, the original, of course)

1. Halo: Combat Evolved
2. Half Life 2
3. Bioshock
4. Rainbow Six: Vegas
5. Call of Duty 4

1. Goldeneye (N64)
2. Nightfire (GCN)
3. Bioshock
4. Halo: Combat Evolved
5. ---------

I can't even think of 5 FPSs that I've liked...

1.) Goldeneye

2.) Wolfenstein 3D

3.) Doom II

4.) Doom

5.) Unreal Tournament

My games may seem old but I don't play many console FPS as I think the controls are broken. And my computer cannot handle any FPS's which have come out in the last 5 or so years.

Quake 2
Quake 1
Duke Nukem 3D
Doom 2
Doom

1 Killzone 2
2 CS:S
3 Cod 4
4 Bioshock
5 Red Faction