I've voted for Ultima 10. I missed on that series when I was young, but I like what I hear about it:
Swen Vincke is determined to put a little bit of Ultima 7 into every game Larian Studios creates.
www.pcgamer.com
"There was so much freedom [in Ultima 7]," Vincke says. "It was non-linear, and you had to interrogate characters to know what you needed to do. You had a party that reacted to what you were doing. It pretty much fit what my friend had told me about so many years before."
"The interactivity of the environment, using it to solve puzzles, how it all blended with the illusion of walking around in a world," Vincke says. "It's something that didn't go forward. If you take Baldur's Gate, it had lots of dialogue reactivity, but the world was very static."
"I only remember the things it [the Ultima series] did really well. We're shooting more for the feeling. That sense of entering a world where anything is possible, limited only by my own creativity. That strong motivation to do things because there's a storyline driving me forward, and that agency to impact all the denizens of that world."
If someone could create a game inspired by what Vincke discusses, and this would be a separate game from Larian games (you know, the more, the merrier!), it would only be cool!