Developers GSC have sacrificed certain aspects of their grand plan in order to create a tighter experience, so those expecting driveable vehicles and a completely sandbox world may have to look elsewhere for their thrills. There's an unofficial mod - Oblivion Lost - that adds some of the omitted features back in, but for what it's worth, I think it was a good decision to draw some lines. This is a game already rough enough around the edges without complicating itself further, and as it stands, Stalker manages to tread its tightrope of design rather admirably.
While it's by no means the definitive FPS/RPG statement, Stalker deserves real praise for its careful delivery of an unrivalled, bleak atmosphere, and for providing final proof that quality games don't have to be about flashy, Hollywood cut-scenes. It's skirting greatness, and though it doesn't quite realise all of its ambitions, it could still be one of the most memorable videogames you'll play.