The Sims 3 is the third part of its series. Like all Sims game, it allows the player to control the life of a person or even a whole family.
Before the main game starts, the player has to create his or her character, called sim. The player can choose to play as a single character or a family. The game allows full customization for each sim. The player chooses their gender, age, race, and body type, as well as their traits that influence the sim's in-game behavior. The traits help sims to learn new skills that will be useful in their job and social life. The player can also choose to set all settings to random. There are also settings that define if the sims will age, and how fast.
The game introduces the open world that lives on its own even when the player doesn't interfere. Unlike in Sims 2, the world is seamless and there's no long load time when you travel it. The sims themselves became more independent and require less player attention to stay alive. Sims 3 is less oriented towards "tamagotchi"-like life-sustaining and more towards actually living the sims' lives, such as going to work, attending parties, making friends and flirting. The sims will occasionally have wishes, and fulfilling them earns the character more happiness points.
The building mode didn't change much since Sims 2, but the game introduced a few additional options. Most notably, elements don't have to be aligned to a grid anymore. The player can place them diagonally at any angle.