Recommend any fps game

Call of Juarez Gunslinger, Rage - both are underrated games, but definitelly worth playing. Nothing more to add, everyone before me suggested good stuff.

This might sound a bit on the obvious side but:
System Shock 2
It's one of the best games ever made. While it might look a bit dated, it still plays great, has a great atmosphere and it actually manages to out Deus Ex Deus Ex.

Another one that I'm quite fond of is Rainbow Six 3: Raven Shield. It's a tactical FPS, and a great one at that (probably the best one ever made, though Hidden & Dangerous is also quite good).

DOOM
Yes, DOOM, 1 & 2. I actually played them for the first time just recently. Yes, I'm ashamed to admit that I had not actually played the full version of DOOM until I bought it on steam, and even when I played the shareware version as a kid, I did not really "play" it, I just cheated and killed stuff. DOOM still holds up, and with the alternative controls that the steam version offers, it's a joy to play.

Shadow Warrior.
Both new & old, both are great fun. I actually prefer Shadow Warrior to Duke 3D.

the obligatory cod/battlefield stuff
counter strikes
the far crys
fistful of frags is free on steam although it's not honestly that wonderful
on the same side, neotokyo is also free on steam
half lifes and their episodes
l4d and l4d2
medal of honor if you're into the boring military shooter thing
the metro games
red orchestra 1 and 2, along with rising storm, are pretty hardcore/realistic
less realistic but still hardcore are the classic doom, unreal, quake, games
shadow warrior, new or old

Unreal Gold.

Just played it myself for the first time a year or two ago and yet I still thoroughly enjoyed it

Prey is great, my favorite FPS of last gen.

Clive Barker's Undying

Also Painkiller: Black Edition and/or Painkiller Hell & Damnation. Quake 4 and Prey (if you can get it) are really worth a try.

blood 1 + 2!

only one fps you need is minesweeper

Project snowbline that's an old game but the difficult is high so if you want a chalange buy it snd have fun : )

I can recommend Payday 2 if you have 3 friends to play with - kind of pointless to play it offline though...and getting randoms to work as a team is difficult sometimes >.<. I can also recommend Planetside 2 (which is F2P!)- it really captures the epic feeling of a war being waged on an epic scale that so far I don't think any other MMO shooter has. Just my two pennies worth :)

EDIT: I'm a derp and already posted to this once.

Counter Strike, obviously.

COUNTER STRIKE.

Fistful of Frags

Shadow Warrior

FEAR series
STALKER series
Red Faction series
Halo 1+2
Painkiller (first 3 + Hell & Damnation)
Crysis series
Time Shift
Jericho
Star Wars Republic Commandi
Far Cry series
Borderlands series
Return To Castle Wolfenstein
Half Life series
DOOM . + Resurection Of Evil
Quake 4
Dead Space series (this is more action/tps game)
Mass Effect series (this is more action/tps game - 1st one is RPG like)
RAGE
Call of Duty (I prefer the 1st 2 and World At War)
Medal Of Honor series (I prefer the WW2 series)
Bioshock series
Deus Ex series
Chrome + Chrome specforce (not that good but I liked back then)
Metro series
AVP series
Hard Reset

ArmA 3, Insurgency and No More Room in Hell (this one's actually a mod).

Dead Island, Borderlands 2, Bioshock series

Spec Ops The Line, pretty good story , F.E.A.R 1 and 2 , Darkness 2, Call of Juarez series ,except cartels that one blows, and Bioshock series, Dead Space 1. And my alltime fav , unreal tournament 1 and 3 .

any counter strike , source is my favorite

Battleduty 5: Galactic Warfare

Thief series. Period.

Bioshock infinite

cod ghost -