S.T.A.L.K.E.R. had some GREAT mods that did exactly #1(AMK in particular). Iirc there are interviews with devs talking about how they had to tone down the AI’s so they didn’t do everything before the player was able to complete them.
the mod in question changed the game so that loners and bands of other characters would go out and about hunting down artifacts and wildlife, and would report events on the radio. It made the world feel much more active; even if you weren’t present for the shootout between some bandits, you could hear about it on your radio, and even run in to the aftermath (although the bodies are usually cleared of valuables well before you arrive)
So while the game doesn’t consist of much more than shooting, looting, and exploring, it feels like you’re just one of many stalkers doing exactly those things.
Link to a descriptor of the AMK mod
The big thing about AMK for a lot of folks (myself included) is that it simulates offline AIlife (which you can’t see due to SE deleting the IM system), and attaches NPC messages to ingame events. So, for example, if you decided to go down to the carpark and encountered a controller, killed it with a shotgun, and then left just as another stalker approached, the IM system might display a message from him about how he just saw somebody kill a controller with a shotgun down by the carpark. Alternatively, you might get a message from a NPC saying that they’re under attack from bandits, and then go the location they specify and find the bodies of whoever lost the fight. (You also might be able to get there in time to decide the outcome of things.) NPC’s will also send messages across maps-- some Freedomer might send a message saying that he has a nice LR300 for sale while you’re in the Bar, and he’ll actually have it in his inventory if you hoof it over there and find him, for example. It also ramps up/randomizes spawns and allows NPCs to travel between maps.