The key game motif is great freedom of choice of how to play. You are entrusted an entire world — a huge territory populated by various creatures, impacted by unknown and bizarre laws, bearing glory or richness or death.
On top of that, you are given a minimal set of equipment and the story intrigue, an unknown world and complete freedom of action inside it. The dangers in the Zone are not only deadly anomalies and terrifying monsters, but, first of all, humans. Which do you choose — fighting for one of the existing stalker factions, or opposing everyone, or changing temporary allies?
Freedom inside the game world is a basis of this game, the game where it is impossible to play twice the same.