I loved the dialogue system in Shadowrun for SNES. It was pretty simple, didn't really have any branches or anything, but it feels autonomous in a way that's hard to match.

Basically, wherever you talk to someone, certain words in their lines will be in bold. Once you've seen one of the bolded keywords, you can ask any other character about those words. Most of them will spit out a canned response specific to that NPC unless you ask about something relevant to them, but the list of keywords is long. It makes it more than possible to play the game several times through and miss certain things. There are runners you can only hire if you get the right keywords, even parts in the main story where it takes a little wandering around trying different things to get the keywords you need or figure out where to use them. Some keywords are basically dead ends, only mentioned one or two times, maybe only in the conversation they're found in, but others will come up again and again.

Shadowrun in general felt very open as a game. Even though it had some barriers to progress before being able to go everywhere, there's a huge amount of freedom in general.

For its time the amount of freedom and depth in the same package was not at all the norm.