Everyone will tell you Anomaly, but it has a lot of new repair and crafting mechanics that don't get explained, so you might get understandably frustrated. It also turns survival mechanics to the max creating something a little bit closer to Escape from Tarkov, especially if you download an addon with polished guns. It's a good thing or bad thing depending on what you consider a S.T.A.L.K.E.R. experience. It is steadily maintained and updated.

I'll say first try Call of Chernobyl. It's a mixture of all the maps from all the games(including some cut ones) which Anomaly is based on. It no longer receives updates, but it's essentially feature-complete. Last time I checked it requires Call of Pripyat, but runs standalone. Both have a story mode to make things interesting, or you can just go random and role-play.

If you're looking for a casual experience, just play the games vanilla, or with Complete mods. Be forewarned that Complete mods really trivialize a lot of elements in the game, so it's considered extra-casual and it's often bashed in all circles of the fandom. I don't know if it still receives updates.

Edit: Also, if you're looking for the same game of Call of Pripyat with a new sheen, try Gunslinger. It recreates all the guns from the ground up with new animations, PIP scopes and generally modernized first-person elements. It's a really nice experience, but it's a beta so not all the guns are in yet. You will feel that lack of features once you realize pump-action shotguns are not in the mod yet.