Pripyat feels like a better game but with a weaker story than the first one. It is more focused on the urban warfare for the last half of the game so if that's what you were liking about the first this one goes really heavily into it. The recreation of Pripyat is very creepy and almost identical, very weird going into buildings that you've seen on film from the initial footage of the disaster and subsequent video tours of the area. It definitely feels like a smaller game but does not have the initial "you with a crappy pistol v. 8 bandits in a farm complex" starting roadblock that the first one had. Every time I replay STALKER I, for some reason, always turn down that guy's help on the first mission without even noticing and then get stuck with the autosave that happens immediately after and have to clear that area solo. I remember always going back and checking the difficulty setting in game and almost uninstalling a few times out of frustration because normal made for one of the most difficult games that I have ever played.
I heard that the third one is really bad and not really in tune with the other two at all so just skipped it. Pripyat is fun but it really makes you want to run through the first one again.