gameon: Do they all need to be played to understand the story, or are they stand alone?
Also what order are they. Are any of them prequels?
I've been interested in the stalker series, especially because of the "real world" graphical setting. But it would be annoying if it was tough to complete because of bugs.
You can play them in any order, really. Clear Sky is something of a prequel to SoC, but not by much. I wouldn't say you needed to play that one first. If anything it might work better the other way around. Personally I found weapon mods that increase the stopping power to be vital for these two.
Call of Pripyat is easily the best of them. Larger areas. More survival orientated, what with the blowouts. It's not at all connected to the other game, other than the same factions and some of the same characters. I'd say at the very least you owe it to yourself to play this one. It's one of the absolute best FPS out there of any type, or era. I'd say that the Complete mods for all three games should be considered vital.