Barring technical issues with Windows 8 aside, this game is actually quite fun to play with for the first 100 hours for any Sims fan. You get to customize your ruler and his/her plethora of "councilmen" who will fill up a number of important jobs within your "kingdom" (it's not really a kingdom really, it's more like a village). You get to control each individual hero from doctor, knight, bard to priest in individual character "mini-episode" quests, as they try to balance completing their overall quest objective with daily tasks/chores. Gameplaywise, it's very quest-driven. So if you're not a big fan of quest-like gameplay a la The Sims 3: World Travels, this is not the game for you. But if you're a huge fan of RPGs and medieval settings, you would find tons of fun with the quirky stories and charming characters.
But like The Sims 3, whose engine and UI The SIms Medieval is based on, it suffers from many of its faults. Things like the forest, cave or marketplace are treated as "workplaces" which your medieval sims disappear into for a few hours with only flavour texts notifying you of the goings-on within. It's all indicative of a lazy game-design that leaves you with rabbitholes to fill your imagination with what is happening by telling you rather than showing you. There is no transportation, so expect to spend half of the time watching your controllable character walking across the village.
Because the world is smaller than the standard Sims 3 world, there is not much lag or crash-issues despite the Open World, thankfully. But do expect some object loading lag, especially if your sim has to walk through certain short pathway areas (e.g. the castle) to get to other destinations.