There probably isn't a lot of you here that are fans of the STALKER series
I fucking love that series. Besides VC:MP, it's pretty much my most-played game. There was a new mod called Call of the Zone released earlier this year which is definitely worth playing - it's almost like an entire sequel, combining the best elements of all three games in the series.
I'm a big fan as well, I own physical copies of all the official games, and am currently passing time on the Anomaly mod, but I've also played Call of Chernobyl. There's been talk of STALKER 2 allowing 2 player co-op, if you grab it when it comes out we can play together
About the game itself, I don't think there's a single title out there that can give you such a feeling of immersion, the level of both feeling pathetic at some points, and the level of empowerement that the game gives you when you navigate its many obstacles. And the AI is just a story of its own. The game basically makes it clear to you that life in the Zone would carry out as well without you, with every npc on the entire map getting his own tasks, doing his own thing and going his own way. What they did with the A-life system is as much ground breaking today as it was when the first game released in 2007
Lost to the zone.
edit: For anyone interested in this game, you can now pick up both Call of Chernobyl and Anomaly for free on moddb, they are now standalone titles
https://www.moddb.com/mods/stalker-anomaly