I'm sad GSC are shutting down.
Stalker was the game I played before I met EVE. I remember the first time I encountered ghosts in the game and I literally jumped out of my chair. Matariki laughed at me, and then complained that all my twitching during gameplay was shaking the shared computer desk. I finished the game (one of the real endings), and then went back and finished it again trying to find the false endings.
It was so goddam pretty. I remember sitting staring at the mist rising over the valleys as the sun came up, until a dog pack ran up and killed me.
Then I modded it, Modded it to heck. I made it so that a center of mass shot from a rifle would take most people down in one shot. I stole from mods liberally. I set one version up so that all the bandits had AK47s instead of MP5s - that lead to an exciting first few fights, until I recovered an AK47 myself that wasn't rusted all to shit.
My favourite mod was probably the AMK 1.4 mod, put out by a bunch of russians - it added in Blowouts again, and anomalies moved during blowouts, and you didn't start with an anomaly detector.
Then I discovered things that were in the original, but masked by their anomaly detector. When you get close to most anomalies, there is a bass hum that puts the hair on the back of my neck on end. Walking through that landscape (familiar after quite a few play-throughs) and knowing the anomalies had moved, and then getting that visceral feeling of dread just before walking into a trap was like playing the game anew. Every time the wind came past and blew the grass around made me check to see if it was an anomaly, or just the wind. Fantastic.
It was buggy. They patched it a lot. But the atmosphere was the best/creepiest in any game I'd played before or since.
Stalker 2 (Clearskies) had a much better set of mechanics, but the atmosphere just wasn't the same. I don't know if that was the game, or me.
Stalker 3 (COP), which I had to import privately (because they didn't apply to get a rating here, which meant it couldn't be imported for sale) had slightly better atmosphere than Clearskies, but the world was slightly less dense, and they tried to put a bit more scripting and quests into it, which lost some of the specialness of the first one for me.