Game World Navigator's interview with Oleg Yavorsky at KRI 2009, with gameplay footage:
http://www.youtube.com/watch?v=LxqVA11rZU0&fmt=18
Speaking about gameplay in general, we expect it to take about seven hours to pass the main storyline and, maybe, twenty-twenty-five hours for free gameplay. In addition, I can tell you that after the game ends, there will be the possibility of remaining there. Not end the game, but continue in free-play mode.
There will be a minimum of underground locations. That is, you will mainly run around over the motherland. There will be a kind of caves, some underground mini-levels, but it will make up, maybe, five percent.
Anomaly locations will change somewhat after blowouts. Also, artifacts will regenerate, since our good NPCs will go around in squads and collect them. That is, the player will compete with stalkers in who collects more artifacts. We changed all the monsters a bit. That is, we tried to make combat against them more interesting than it was previously. All monsters will become more mobile, more diverse in their behaviour, their habits. For instance, chimera, fairly harmless during the day, will become quite challenging to fight at night, when all monsters activate. Therefore, every monster has to be seen, understood, studied to find an effective measure against.
The main difference of quests in Call of Pripyat will be in that they no longer regenerate automatically, as they have been previously. They are crafted by designers in advance. This makes each scene unique, makes it more presentable and interesting for the player. For instance, there could be a quest to... [you will find out what kind of quest there could be in the June issue of "Game World Navigator"]
-source: gsc gameworld forums | translated by Don Reba-