[In this fake series (that maybe will become a real series if I or others feel like it), I turn the Destructoid original series "Games Time Forgot" on its ass and instead discuss time periods that games just don't seem to explore.]
Thanks to stories of King Arthur and his favorite magician, Merlin, it's probably unlikely that we'll see any sort of realistic games set in the Middle Ages. Medieval times on our own world have largely been forgotten, instead replaced by created worlds where magic can lend a sense of wonder to an otherwise unsophisticated and dreary existence. For this reason, making a game without these elements might be considered too risky by developers or publishers.
We still have games that are somewhat similar, at least. Bioware's Dragon Age promises a low-fantasy tale with plenty of maturity, and we'll always have the occasional RPG or strategy game that lets us visit castles and swing swords.
But I know that a great game is just waiting to be made here. Despite a lack of realism, I think games like Assassin's Creed proved that games set in historical periods can indeed work in the hands of a skilled team. And, come on, who doesn't like knights?