Which FPS series has the best single player campaign?

[TruckOSaurus]

ithis said:

Doom 2 baby.
Almost no story, but the levels just flow one after the other.

Edit: So as a series, the old DOOM games.

Later edit:
Freekin specify the era if your thread title is explicit enough to answer directly damn it.

I'm one of those crazy guys who still believes in reading the OP, so no.