PC Shooters you MUST play sometime.

Here is the list of games that must be played, start to end. I will include only Single Player based games, multiplayer can come later :P. 

1. Half Life 2 – Probably one of the best overall experiences you can get from your PC. A solid storyline is backed up by good graphics, the occasional piece of atmospheric music and challenging AI.
2. F.E.A.R. – One of the scariest games I have played, mainly due to the very creepy little girl, and has a solid story to keep you guessing till the end (and what an end). Also got some of the best graphics you will be able to find in current games (in slow-mo looks even BETTER!)
3. Far Cry – Although quite an old game (relatively) it still supports some of the largest and most detailed maps ever found in a game. Loading screens are few and far between. This dense environment supports eaither stealth or “run in guns blazing” approachs, although a mix of the two usually works best. Add together some tough AI and an interesting story, and you got yourself a fine game.
4. Call of Duty 2 (plus original+expansion) – If you like WWII shooters, you can’t get much better than this. It really makes you feel like you are fighting an an army, and not solo, like most shooters do. The graphics are top notch and the sound effects really makes this game exciting (especially with surround sound). The varied campaign as playing as British, US or Russian forces lets you say all sides and keeps you itnerested in the people involved.
5. Darwinia – This is one of the most innovative, absorbing and emotional games I have seen in a while, and although not a shooter, it doesn’t  really fall into any genre. Seeing the little Darwinians mourn the dead, and jump for joy at victory, makes you really feel for them by the end. And yes, the graphics are meant to look like that! (They DO live insde a completely digital world…)

I only have the 5 games at the moment, mainly because I am very picky. More will eventually come as I think of them, and feel free to give your ideas in the comments section.