An interesting, innovative base concept disappointingly executed.
That isn't to say the game itself is plainly terrible, it's very nearly passable on its own. The visual experience of the game is certainly appealing (even if it can be a little hard to make truly unique-looking faces for your sims sometimes) and it does absolutely fit the medieval theme with the added twist of the usual cutesy charm of The Sims. In fact, some of the new features added to gameplay aren't too bad at all at first and give each sim you play a definite, unique feel from the others.
As the player, you don't just play any and every sim, in fact most of the sims you see running around in the game are non-playable, but the story of the game isn't about them, it's about the "hero" sims you create when building their respective buildings. These heroes complete quests and go about their daily business specific to whatever their job is. The theme of this daily business is enforced by a set of two random jobs per day usually unique to that hero sim. A knight has to get in duels, train guards and do other knightly things while a physician has to heal patients, collect leeches and herbs and do whatever else is befitting of a medieval doctor.
Note that I used the phrase "has to". There is, lamentably, very little that is truly optional in the game. While yes, your hero can do extra job tasks if they want, they do virtually nothing to add to that hero's experience and overall enjoyment. What's worse is that you'll generally be too busy with your two smaller job tasks and the much larger quest at hand to go off and do things purely for their own sake. There's even a system in place to enforce staying on-task. Failure to complete your assigned daily duties or maintain a good pace of completing quest tasks will give your hero a negative moodlet (basically, they get pissy and sad while also not being as effective at doing whatever activity they undertake). Effectively, you're punished for playing this version of The Sims in the usual, choose-your-own-adventure playstyle, something that would have made this game infinitely better.
Still worse is that the confining nature of the pace of play isn't the greatest detracting feature of the game. In theory, the "goal" of the game is to complete quests to gain little points with which to build additions to your kingdom. These additions can be buildings that provide housing for new heroes, add passive benefits to your kingdom or are annexations of other, forever-left-unseen kingdoms that provide other, passive benefits to your kingdoms.
Eventually, you fill up your little kingdom with buildings and heroes and you'll start getting a little thin on quests, but worry not! You can take one of your fine heroes, do a little questing and recruiting of people from around town, and next thing you know, you'll be sailing off to found your own kingdom! A kingdom that... Looks exactly the same as your old kingdom... Except it has none of the enhancements from your previous kingdom except for the monarch you brought over... Oh, and if your monarch had any awesome equipment in their inventory, that's totally gone. As if to drive home the sudden disappointment, it is exactly the same as the starting map, down to the finest detail. The game itself almost taunts the player when it comes to this, too. When you start up the game, there is a map of chained-together achievements, whole kingdoms where you can go and build a new kingdom with specific goals in mind. Ultimately, this cements Medieval's statement that you, the player, are not the one making the decisions around here.
Even the enjoyable customisation of previous installments is largely stripped from Medieval, what remains is a joke compared to what veterans of the series are used to. You can wallpaper the walls and add some new furnishings if you're so inclined, but the entire construction tab is long-gone. This has the effect of making the repetition of starting new kingdoms even more brutal, as you find yourself toiling in the same lands, with the same quests, in the same buildings and all that changes are the characters in that world who, as a rule, are more often impacted by the world than they impact it.
There are things missing from Medieval. Many of them are obvious decisions to make the game something other than "The Sims but in the past" that went horrible wrong, but some are something worse, something more unpleasant and harder to pin. The entire experience after the first five hours of gameplay when the charm wears off is disappointing, it falls flat and completely fails to live up to the game's initial aims.