S.T.A.L.K.E.R.: Clear Sky

  S.T.A.L.K.E.R.: Clear Sky is a prequel to S.T.A.L.K.E.R.: Shadow of Chernobyl where you play the role of a mercenary named Scar.  You are escorting scientists through "The Zone" when out of no where, an Emission hits. An Emission will kill anything in it's path unless you are in a shelter of some sort.  And there was no shelter for you or the scientists.  They died, but strangely you survive and are rescued by Clear Sky personnel.  Clear Sky is a faction dedicated to the exploration and understanding of "The Zone" and regard it as a gift to humanity.  After you recover  Clear Sky employs you to secure their position in "The Zone" as it is being  threatened by bandits and the like.  Then later on to discover why "The Zone" has become so unstable.
  Talk about a survival game,  I survived this game by the skin of my teeth.  I can not remember how many times I came to a group of people after suffering from exposer or combat bleeding and damn near dead hoping someone had a bandage on them I could buy.  Or anti-rad to cure my rad sickness.  I seriously only made it by scavenging anything and anyone.  I barely traded goods.  Any weapon or ammo I needed, I got from dead stalkers.  My Vintar BC I found off an unfortunate ally fighting Zombies.  My SVD I looted off a Freedom corpse after a firefiight with Duty(You said Duty). You get the point.  I  enjoyed the challenge and enjoyed being a merc in this game.  Though I recommend savoring the game and not rushing through it like I did.
  Play this game now.