You know, I gotta admit that I rather liked Ultima 8. It was the first of the mainstream Ultimas that I saw (but THE first Ultima I ever saw was Martian Dreams). However, I didn't like it enough to actually finish it. Same goes for U4,6, and 7. Though I almost finished U6... because it used the same engine as Martian Dreams (which, as far as I'm concerned, is the best Ultima game ever...). Of the non-mainstream ones, I also saw Savage Empire, one of the Underworlds, and of course, Martian Dreams.
Just out of curiosity, how many people have played Martian Dreams? It seems to be... well, not very well known.