Comparison between The Sims 3 and The Sims Medieval

The Sims 3 and The Sims Medieval use the same engine, so they may seem somewhat alike, but they are very different games.

The basics
The Sims 3, like previous games in The Sims series, is set in a modern era. While players have always been able to use custom content to simulate a medieval setting, at least to some degree, the games themselves presume a modern society with refrigerators and stoves, computers and telephones, etc.

The Sims Medieval, as its name implies, is designed to simulate a medieval setting. Therefore, it does not have modern features such as carpools, taxicabs, and telephones that would need to be disguised or worked around.

Create a Sim
When creating a Sim in The Sims Medieval, one major difference from The Sims 3 is the clothing and hair that is available.

Personality
The Sims Medieval keeps the trait system that was introduced in The Sims 3, and adapts the traits to the medieval setting. At present, it appears that there are fewer traits than there are in The Sims 3 base game. While Sims in The Sims 3 have between two and five traits, depending on their life stage, Hero Sims can only be given two traits and one fatal flaw, which can be considered as a very negative trait.

Motives
In The Sims Medieval, the number of motives has been reduced to two, Hunger and Energy.

Marriage & Families
In The Sims Medieval, NPC Sims do not become selectable when they join a household, even if they marry a selectable Sim. Also, all children are NPC:s. The children don't grow up, so there are no Teens in the game. This is a major difference not only from The Sims 3, but The Sims and The Sims 2.

Jobs
In The Sims 3 and earlier games, the pre-made careers were modern careers for a modern era. While careers could be modified, and custom careers could be created, the basics remained the same. Sims would enter a career, get paid on the days they worked, and gain promotion by building skills, making friends, and having good job performance.

In The Sims Medieval, the jobs that are available to playable Sims appear to be linked to the various classes of Hero Sims. It appears that Hero Sims are created to fill specific jobs. So, instead of Sims starting out unemployed, a player would specifically create, for example, a monarch, blacksmith or spy. All jobs have a medieval tone and flavor. For example, physicians use leeches to treat their patients.

One notable difference is what happens to Sims who skip work too much, or who have bad job performance. In The Sims 3 and earlier games, that could result in demotion or firing, but nothing worse. In The Sims Medieval, it could result in fines, being put in stocks and pelted with food, or even execution in "The Pit of Judgement".