Gamasuta has an article in which they ask some game industry professionals which FPS game made the biggest leap in the genre. Quote:
"In August 2006, the editors of Gamasutra asked its readership of game industry professionals to chime in and vote for which game in the first-person shooter genre "brought the genre forward" in the biggest way - whether it be an early game that helped define the FPS, or a more recent one which took those core ideas and developed a more rewarding experience than before. Specifically, we asked: "Which first-person shooter/action title over the entire history of the FPS game do you think has made the biggest 'quantum leap' in the genre, and why?" "
The developers included in the article is a long list which I won't list in full detail but some of the quotes are from: Alex Swanson, GarageGames, Inc.; Toni Petrina, Cyprox Studios; Patrick Redding, Ubisoft; and many others. The games discussed are Alien Vs. Predator, Descent, Deus Ex, Doom, GoldenEye 007, Half-Life, Koronis Rift, Marathon, Quake, System Shock, System Shock 2, Tribes, and Wolfenstein 3D.
What I found peculiar is that Halo was not named in the article, I would have expected it to at least get an Honorable Mention since it was and still is one of the most popular console FPS game to date. This may not represent a quantum leap forward but I believe it is definitely worth a mention since it practically drove the Xbox console sales during the first year. Me and many of my friends bought the original Xbox in part to play Halo. I have not played all the titles listed but I am starting the process of hunting them all down to give them a try. I enjoy the historical side of gaming as much as I do the next-gen hype and hope to add these games to my gaming experience.
I put the above list of games in alphabetical order, if you want to find out what game was voted number one, you will have to go read the article here: The Gamasutra Quantum Leap Awards: First-Person Shooters