Chivalry and Sorcery: The Rebirth
This is a well-researched "historically-based" game, rich and deep in itscomplexity. It captures the flavor of medieval times as well or better than most other games. If you can get past the complexity, it will be worth it to do so.

Common Ground I
Getting frustrated that your playes don't do what you think they will. Don't know what to do when they don't know where to go? Here is a partial and useful solution to that problem.