Ultima 7 is basically the dogs bollocks. It's actually two games, the first is the Black Gate, a return to Britannia after two centuries of abandonment by the Avatar (you,) a spiritual and ethical hero who represents eight virtues. The world has changed in his absence, and all is not what it seems. The Black Gate has an expansion built in called the Forge of Virtue, where one can truly master the principles they live by.
The second part of Ultima 7 is the Serpent Isle and its expansion, the Silver Seed, which I won't spoil for you. It's a more linear experience than the first game but still a masterpiece. They're both absolutely huge games, fine narratives in living, breathing and changing worlds. They spank fairly much every modern game, but for the combat which is largely automated and not very satisfying. Though there are tricks to it, and spellcasting is tremendously powerful and fun if used correctly.
This is a living world, and you will need to prepare, eating food and drinking. A bedroll for sleeping in the wilderness. Swamp boots to stop infections when travelling through marshes etcetera. Exult always worked very stably for me, a lot of people reported a disappearing item bug, never had it personally.
The Underworlds are creatures of a very different stripe, the first great 3d engine that absolutely spanked Doom and everything else, the Elder Scrolls are based off this but nowhere near as good. The first has you (the Avatar on an unsung trip to Britannia just before Ultima 7) being thrown in the great Stygian Abyss, a superdungeon that has become home to a colony. Your goal is to clear your name, resolve a mystery and save the maiden fair. Or so it seems at first.
The second game is set between Ultima 7 the Black Gate and Serpent Isle, and is truly an adventure through a labyrinth of worlds. Both games are utterly jaw dropping if you think about what they accomplished technically, feature, content and narrative wise. Far ahead of the curve, and we still haven't caught up in my opinion.
Oh one thing, the manuals, maps and booklets that come with the game are not optional, you will have to read them and keep a notebook and pencil handy as well. I envoy those of you whom are about to set foot on the path of the virtues, may Courage, Truth and Love ever guide you Avatars.