The only Ultima games I played fully are VI, VIII and IX. Sadly, I missed VII at the time, I tried to play it many times but I just kind of lose interest as soon as I enter Britain. I have kept it installed on my PC for like 10 years, always ready to get back to it but...
VIII was too arcade for me, it lost much of the RPG aspects of Ultima, and IX was too formulaic - go there, close gate, go there, close gate - as opposed as VI that was a real, breathing world... but it wasn't as bad as people paint it.
VI was awesome. An incredible game full of little stories that you need to discover for yourself (the pirate map, for example), huge world, the whole sailing thing with a sea full of dangers that screamed "ADVENTURE" and a great story with political implications. I think the dialogue interface (you had to write words and see if the other character reacted to the word you used) while obviously clunky added a ton to the believability and especially to the sense of discovery of that game. The game didn't hold your hand, you had to work it out for yourself and it was a very rewarding experience. You heard someone casually mention a pirate treasure and... hey, I wonder if that drunkard old sailor that comes to the tavern in the evenings knows anything about it? No, he says doesn't but maybe let's follow him around at night and...
The problem with those games, in this era, is that you have to live in the game's world. You just can't be a passerby and complete a checklist in one place before moving to the other. You have to spend time with the characters and the world. But now we're trained to quickly consume product->buy next product, so I doubt many people would find them enjoyable.
I played some UoL, but not too much as I was more invested in DAoC and the PK system bothered me, great game and I have memories of a late friend in there.
I also always wanted to play the spinoffs: Martian Dreams and The Savage Empire, they have a fantastic setting and looks really interesting, got them all on GOG, downloaded dozens of time and never played. I wish they remade them.