Lost in Blue was somewhat demanding. I still liked it for a while though. I think I prefer UnrealWorld to any other survival sim I've dealt with.
It's probably not what you're looking for, but there is an OLD game, probably early 80s or so. Called Visions of the Aftermath: Boomtown. It basically gave you randomly generated Post Apocalyptic worlds that you would spend your days travelling around, gathering supplies, looting buildings and fallout shelters and trying to build a new life for yourself. (In some game modes there was some diplomacy involved and you were encouraged to form alliances with other survivors.) Alas, I never got it to work completely right. A lot of the game was actually the manual though. While the game would give you very basic generalized things to work with, like "Food, water, fuel, parts, etc." The manual was written as an actual survival manual would give you ideas of the things you could do with them. The only one I remember clearly was a detailed description of how to make an electric generator waterwheel out of an old car alternator. In game this could be done with some "parts" and I think maybe one other resource. But the manual gave you something to fill your mind with an imagine.
On the surface it was a really simple game, but could get very deep if you kept at it.
Also, it could be played, hotseat style, with up to 4 players.