Well, reading my comments indicates i totally failed to address one aspect of Ultima V that made it vastly superior to all the previous games--namely, the storyline. Ultima 1-3 had stories, but the events and impact of them were contained almost entirely within the documentation. Ultima IV was strangely plotless--it was a quest of self-improvement, but there wasn't really any compelling need for the world to have you as Avatar. I would summarize the back story of that game as, "Everything's going OK I suppose. Let's find someone to be the Avatar!"
In Ultima V, by contrast, the first thing that happens (granted, in a cutscene) is that you get attacked by a Shadowlord. They also take over towns, and Blackthron harasses you on a regular basis; guards demand bribes, and so on. Unlike the previous games, there's the sense of impending disaster and the well-being of the world hanging in the balance. The illusion breaks at points (like any game), but it's there for the first time. Ultima VI's major failure is in this regard; I still can't get over the moron that makes you build and play some panpipes before letting you save the world; moreover, hardly anyone cares about the Gargoyle threat in general. At least in Ultima IX, Katrina apologizes for wasting your time!
I would also disagree with a commenter who said Ultima V's combat was insufficiently strategic and thy preferred Ultima IV. I thing the opposite; for most battles at the end of IV, I just repeatedly hit the A key and the up arrow because the massive barrage of magic arrows and wand bolts and whatever pretty much cleans the board of all enemies. As for the argument that a Shepherd or a Fighter is the best character class in IV because you can ge them to level 8 more easily, I say there's no particular reason to bother. Even in the abyss, everything was dead before my uber-Shepherd gets in melee range, and besides, touching those orbs is tedious.
I also got some other comments! Someone said that the item in Serpent Isle which trades for the ice wine was "obvious" but can't remember what it was; I say that such an item does not exist. Finally I was attacked for not showing Ultima Underworld sufficient love, but I maintain that I was fairly positive in my comments :-P If I'm overly critical, it's only because criticism is more fun to read than positive comments.
Hope everyone has good holidays, or at least those of us in the United States. I am on vacation so I may publish more this week.