Look, nobody worships at the altar of Lord British more than me, and you can't put into words what a breakthrough Ultima IV was at the time. It set me on the path to writing games for a living. I played it again and again. It literally Changed My Life.
But it isn't playable now. The controls make no sense. The dialogue is bland. All of the little UI tricks that make RPGs accessible (tooltips, in-game maps, pathfinding) were not yet invented. And, and this is really important, everything that Ultima IV introduced everyone has done far better. Ultima IV had an epic quest and morality woven into the game, which was amazing at the time. But everyone does those things way better now.