Recs.
Updated
A MicroProse classic from 1992, runs on XP, Vista and Windows 7.
Also available on the Internet Archive.
SpecsUpdate
Pros
Pro True to the history
This is another face of this game's attempt to be "realistic". While one might argue that its "magic" system, while surely enough based on the tales of the time (see "True to the folklore" pro), can never be considered realistic, when we ignore the magic, this game is a decently realistic representation of the Dark Ages. The armors and weapons, their use and their resistances and weaknesses, the society, the whole world, everything is built trying to be faithful to known history.
Pro True to the folklore
This is a true rarity. Things work as (we suppose) people of the time tought they worked. If your characters have enough virtues, they can ask for help to Saints, who can grant some minor or major miracle, and every Saint has his own area of work. Alchemy needs, more often than not, rare ingredients and is even rarer to put your hand on some good recipes, this without even taking in account the philosopher's stone. And, without spoilering too much about single events and quests, being "modernly open minded" can lead your party to some consequences.