If you ever want to revisit playing the rest of the games, they are all available on gog.com and setup with Boxer or Wineskin and a nice installer plus manuals, a helpful forum of other players (they have a forum for every game on the site) and they are cheap. The series really reached the pinnacle of greatness in my opinion with the epic two part Ultima VII: The Black Gate followed by Ultima VII: The Serpent Isle. The GOG releases even include the original content packs too which is very cool. Maybe you already know all this stuff but the graphics on that title blow away completely everything that preceded it. Totally awesome Ultima greatness. While I am on a roll here, both the original Underworld games can be had there as well. The only title they don't have configured to run on a Mac out of the box is the final game, Ultima IX which I haven't gotten to yet but reviews be damned, I will play it. I have to. I tried when it was new but back then you really needed a voodoo card for it to even run right at all. I tried playing it, valiantly, and I even had a little fun too despite what others say about it but my old system just couldn't hack it well enough for me to journey onward.
Oh, and last I knew Ultima IV is a free download on GOG. There are number of titles they give away as incentives to create an account with them I imagine. You do want to be virtuous don't you? Of course you do!