I'm about 40 and am usually grouped as a millennial (at least for the common purpose of blame, e.g. killing cinemas), though I somehow missed Baldur's Gate; played the hell out of the Ultima series though!
The Ultimas were (mostly) wonderful, especially Ultima 7, but I don't think there's anything particularly valuable about the "IP".
It was really about Garriott exploring innovative ways in how to translate the tabletop RPG experience into a computer game. You don't need an Avatar or Britannia to pursue ideas like Ultima 4's virtue system or Ultima 7's interactivity.