Gamespot posted a designer diary for Stalker where Alexei Sytyanov (designer) talks about the game, storyline and such. Here's a snibblet:<blockquote>The locations and levels of S.T.A.L.K.E.R. form one global map where players are free to roam without any directional limits. This freedom extends in to the cities of Prypjat and Chernobyl, deep in to surface and underground laboratory complexes, and in to the vast territory of neglected military bases and testing grounds that litter the Zone. </blockquote>And there are also some great screenshots to look at here.
Link: Stalker Designer Diary
Link: Stalker Designer Diary