>>4029
Be sure to check the specs on steam. Although I'm not the person you asked, I can recommend it. It will take some getting used to, but if it hits home for you it is a unique and very satisfying experience.
Play through S.T.A.L.K.E.R. Shadow of Chernobyl first. It introduces you to the series, tone, difficulty and story - and is a good game in its own right. Afterwards go to Call of Pripyat, which I personally think is the best in the series and gets close like you're actually in the Zone.
You can safely skip Clear Sky. It is something of a black sheep, though it has some nice set pieces and arguably the most cohesive plot of the series.
If you do want more, but don't want to mess with Clear Sky, there are a ton of great mods for Shadow of Chernobyl and Call of Pripyat. I can personally recommend Lost Alpha for Shadow of Chernobyl, which adds removed content back into the game, rewrites the storyline, adds a ton of locations and balances gunplay.
For Call of Pripyat keep an eye out for Call of Chernobyl, which adds the areas from the previous games (Shadow of Chernobyl and Clear Sky) to the game world. Although there is no additional content (no storyline) to these areas, they're fantastic for just strolling around and cheeki breeki'ing.
Fair warning that, with the cancellation of S.T.A.L.K.E.R. 2, the series is considered in limbo. After Shadow of Chernobyl a big part of the team left to make Metro 2033. The remainder left after the publisher hogged the rights to the franchise. They're currently working a spiritual squeal to S.T.A.L.K.E.R. known as Survarium, an mmo fps.
All in all, I personally consider the series to be pretty /late/-core.