Great storyline and locations that don't let you get bored for a second.
The one thing I didn't like is the fact that the guys the game is throwing to you are like...thousands. Which could have been fine, if it wasn't the fact that you can kill up to six or seven baddies before they manage to hurt you badly enough to force you look for cover. Bad guys just tend to die even if shot in the toe (well, maybe not that easy, but you got my idea). I liked better the Medal of Honor approach - much less, but tougher enemies. That's when head shots really count.
I couldn't miss mentioning the Pripyat level. Though it left me with the impression that maybe the level was not planned until S.T.A.L.K.E.R. came out (means: they copied the great idea from the Russians), the mission was perfect in almost every way! And of course the Irish sniper was so inspiring :)