If you haven't played King of Dragon Pass, you really should. It's a difficult game to describe, but a world builder combined with a choose-your-own-adventure is the best explanation I've seen.
The game itself is a civilisation sim at its core: you have to guide a young tribe of people from a small, ineffectual group to the ruling population of the so-called "Dragon Pass". On top of this crunchy layer is a rich storytelling system where you're presented with "scenes" that feature multiple choice decisions.
The great thing is that your decisions aren't just forgotten -- they become weaved into your tribe's overarching narrative and future scenes will be influenced by earlier successes (and mistakes).
When I played the game it had such a profound effect that it heavily influenced the design of my first commercial game, Zafehouse: Diaries.
King of Dragon Pass can be confusing and impenetrable if you avoid reading the manual, but every single aspect of the game is explained in detail within its pages and there's an online wiki to help you if you get stuck.
KoDP is a reasonable $US11.99 on Steam, if you'd like to grab it today. The original is cheaper at $US6 on GOG. I couldn't find a clear description of what the differences are, but I'd say your best bet is to grab the newer release.
King of Dragon Pass [Steam]