The game that put Sid Meier on the map (released two years before 'Civilization'), 'Pirates!' is a game with a shocking amount of depth and variety. While it's not too much less vague then most of the PC RPG's of the era, there is absolutely nothing that you HAVE to do - You can travel anywhere and do anything that you want at any time you want. As a result, the vagueness isn't frustrating because you can learn where everything is with no pressure of having any goals or missions to accomplish. And don't worry - If you think the lack of objectives will make the game boring, it doesn't. There's enough to do- trade with merchants, raid villages, battle and loot ships, and of course fence -that you'll be entertained for hours on end. Though the controls, specifically of the ship, can be a bit stiff and unresponsive at times, this is probably the best sandbox game that could have been made in 1987, and no doubt the best that was.
(I would give this a three-and-a-half, but that's not possible on this particular site.) I haven't yet beaten Ultima IV, and I honestly don't know what the likelihood of my doing so is. There's a deconstruction-process that modern-day gamers like myself must go through when playing a game like this: While I'm used to RPGs where everything is well laid-out, to the degree of being too simple, Ultima IV (and really any RPG from around it's time) are the polar opposite - They're vague, mysterious, and honestly rather unintuitive. I acknowledge the influence it's had on it's genre, and really it's not a bad game- the combat, while primitive, is simple and fun, the world is surprisingly well-realized for the time, and the conversations are interesting to navigate once you get the hang of doing so -but I have to be honest: It's a chore to play today, simply for the fact that it's extremely hard to know what you're supposed to be doing or where you're supposed to be doing. Maybe it'll get better the more I play it, but for now I think of it as a poorly-aged landmark.
