Which was your hardest-challenging fps??

Pariah.

Halo 3 on Legendary... alone. In co-op, it's even kind of easy. But the usual AI partner goes in all Rambo and gets shot within seconds, and you alone have next to no chance to finish that game. I couldn't even get through the first chapter.

If multiplayer counts, then Half Life (1). Some pro-ass wizards are headshotting me even while they face the opposite direction sometimes, yet I can't aim for shit in that game. I might need a crosshair mod to help with that actually.

Requiem: Avenging Angel

Hmm. Maybe Red Orchestra 2. (No idea if the first one was even harder, never played it D:)

All Shooters are pretty doable on each level when you duck/escape enough fights.. I only remmember the easiest of all FPSes which is ofc Crysis1-3 (go with the Future Deagle and kill them all(no idea but C3 yet)) and Rage (1hit mutants in the head with fists)
If I had to say one shooter it would be L4D2 on solo mode, and then try to get the jerrycans.. impossible :D

i think ro2 is hardest and easiest is deus ex human revolution

Iron Front: Liberation 1944

Chex Quest, so hard :P

Call of Duty: World At War on Veteran

Prepare yourselves men! Incoming grenade rain!

hard to choose for me really so i will go with Doom 64, for a console FPS, it gets pretty hectic later in the game

Quake 2 on PS1 console with gamepad, yeah I loved the game that much, and after finishing in PC, I wanted to finish on PS1 once moar. Back then there was no auto-aim etc.

Red Orchestra Ostfront, this game had flat learning curve in time.

Spec Ops: The line on hardest. Especially one level I replayed about 30-40 times

CoD:WaW on Veteran, the grenade spam-fest...

I have to say Unreal Tournament from 1999 against godlike bots. :)

Serious Sam 3 whooped my ass.

<Insert "modern" Call of Duty here> on Veteran(or whatever their highest difficulty was). Mostly because staying behind a wall and instantly getting "ketchup" in my eyes the moment I show my nose out was so utterly boring I didn't even bother learning how I'm supposed to play it properly. Juggernauts and instant-death-dogs didn't help at all.

SS 2. You know... shootin some bad guys on the hood when-
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
And there's like 15 of them on the radius of 5-10 meters

farcry 3.
Sometime this game force me to break my mouse and keyboard.

farcry 3.
Sometime this game forces me to break my mouse and keyboard.

Half Life 2: Deathmatch had some servers with stupid hard coop maps.
Quake 3 for hardest multiplayer game to get into without getting your ass handed to you for a few months

For me I think it's Crysis lawl So hard to kill people e_e

serious sam games