Half-Life for me, no franchise even comes close.

For me Starsiege Tribes. way ahead of it's time. Community mods made it even that much better.

No doubt Halo stole some elements from it

Honorable mentions:
1) Unreal Tournament
2) Duke Nukem
3) Half Life
4) COD
5) Quake

Jedi Knight.

Seriously though of these I’d probably pick Call of Duty. Even today you can clearly see they’re quality games for what they are. Plus the first two were amazing and two of my all-time favorites. I’ve not been interested in the series anymore since CoD4 though because they became too complicated and multiplayer oriented for my taste. That’s the problem with pretty much all modern FPS’s. FPS’s from the late 90s and early 2000s were just more fun. Mindless shooting, fast paced, ridiculous settings, weapons and characters and no additional BS such as perks and skills and character-levels. Just shooting. The decline in interest for the genre started with Halo for me actually. I thought it was much too slow paced and subsequently was never interested in any of it’s sequels. I know in recent years Doom has provided a sort of comeback of old-style FPS games, but I haven’t played so I don’t know how it compares.

I agree with this one. Even though I completed HL2 and Episode One, it seemed like a major stepback compared to the first one. In everything - the direction they went with this one, gameplay, physics. Yes, it was technologically advanced back in the day, but for some reason I just like GoldSrc games more than Source games. For me Source engine was a step back for Valve and it just made games less enjoyable.

Half-Life even though Valve gave up on it. Half-life series offers the most varied and fun game play with a well integrated story. It's a shame we never got episode 3 nor HL3. Shout out to Resistance 3 for its very half-life like campaign and fun game play. Too bad the first two entries don't really match up and the series was abandoned just as it got good.

Kill zone is a good series with great set design.

Max Payne is awesome, loved the 3rd entry after waiting for it for many years.

Wolfenstein the new order was great, but I didn't really enjoy the other entries in the series apart from Wolfenstein 3D.

The only Halo campaign that kept my interest was Halo 4. I never finished the others, great multiplayer, not so great single player or rather very repetitive single player. Doom also lost my interest. I enjoyed to slower pace of Doom 3, the new ones just feel like battle arenas. I need some exploration and story in my FPS games. I rank Far Cry and Bioshock over Doom and Halo.

I've only played two FPS games.

One of them was COD back in 2008 or so, I think it may have been the 3rd one, whichever that was. I played it for 30 mins and then stopped because I didn't like it.
The other FPS game I played was Bloodshot on the Seag Megadrive. Bloodshot is the only FPS game I enjoyed, so that's where my vote is going.

once you get past the hover boat and obtain the gravity gun it changes the dynamics .

If we talk individually my favourites are HL2, Killzone 2  I rarely play mp  but really enjoyed the mp in KZ2 , both Bioshock 1&2, Resistance 2 for the 8 player online co op Halo 1-3 and Reach  and i'll round it out with cod mw4 and Timesplitters 2.

For me, gotta be Bioshock.
From their powerful atmosphere to their deep storytelling, to their awesome Plasmid-powered combat, they're just amazing experiences.

Doom and Halo are pretty much tied for second place.

Metroid Prime