I just watched all their videos on the website and it looks (purely from those videos) that basically everything is there. The got the day/night cycle, the anomolies, some enemies, vehicles, at least 3 weapons that i could see and a decentish AI. What else are they doing?
It doesn't seem that ambitious to me really. It's almost like taking GTA:SA making it bigger, forcing a FPP and giving it a better AI and giving it a change of setting. GTA:SA worked fine, why not STALKER?
Also someone mentioned that the game doesnt look good, but i think it looks more than adequate. You wouldnt expect a game that has 20sq miles (they claim its that innit?) of area to wander around in will look like D3/hl2, unless it was split into small sections just like D3 and HL2. But that would truely suck.