Other than the main storyline, this game is a clear improvement over S.T.A.L.K.E.R.: Shadow of Chernobyl.
That being said, pretty much everything else about the game is really well done. There is a mystery about what took down a number of military helicopters, and the answer is a fairly big letdown. I will start by saying that the main plotline is pretty weak. I finished S.T.A.L.K.E.R.: Call of Pripyat close to two weeks ago now, but I've been busy between work and travel and only just got a chance to put down my thoughts about it.