I'm actually really into them as of late. I checked the last 5 pages and noticed no one had a thread about them so I thought I'd see if any CSn members have played any of them.
For those of you not familiar with the series, it's set in the area around the Chernobyl NPP called "The Zone". In 2006 a large explosion rippled through the area and soon mutants and anomalies popped up. Groups of treasure hunters seeking rare artifacts jumped the military blockade and began searching and they became known as Stalkers.
In my opinion Shadow of Chernobyl was the best for the atmosphere and story line but, Call of Pripyat had the best gameplay.