A group of stalkers, for the first time, reaches the very heart of the Zone-the Chernobyl Nuclear Power Plant-and triggers a cataclysm on the brink of a catastrophe. An immense blast of anomalous energy transforms the Zone: the once reliable and relatively safe roads are no longer so, the landscape is wiped clean by outbursts of anomalies, and previously unknown areas appear on the Zone map. Stalkers and expeditions perish or end up isolated within the lost territories.
SoC has the best atmosphere. CoP has the best feeling of isolation. CS has the best everything else.
It's more rounded out than Soc, and has a much more developed world than CoP (not to mention the ending in CS doesn't leave you blue balled like in CoP). Also, thanks to the faction war system, CS also has the most replayability.
10/10 would STALK again.