Very fun and knee shaking.
It's a "survival horror" game in which takes place somewhere around the year 2015.
The setting revolves around the Chernobyl disaster in 1986. The player can eat, drink, prevent radiation sickness, and fend off bandits, military squads, mosters, and other factions. You can explore and strike up conversations with any AI that wont attack you in the game. You can make choices like any other Role Playing Game (RPG) and trade items or weapons you may have in your inventory. The game is hard (even on easy) but VERY rewarding. Unlike RPGs with stiff movement such as Fallout or The Elder Scrolls series, movement in S.T.A.L.K.E.R. feels loose and smooth.
TLDR:
Survival horror RPG that takes place in Chernobyl in 2015.
*(I think the gameplay is better than Fallout 3)
*(If you get dizzy playing FPS games like me, you can turn down the inertia in S.T.A.L.K.E.R. It helps a lot.)