In The Sims 3, you do the same things as in the previous installments — you control your sims and their actions and relationships in a manner similar to real life. The game does not have a definitive ending, and you can play it endlessly.
The houses and neighborhoods of the sims are located on a single endless map. Furthermore, your actions outside the home are just as important as those inside it. The game also includes a 'story progression' option that allows sims in autonomous mode to behave as if they are controlled by players: aging, marrying, having children, pursuing careers, building or buying houses, and so forth.
In the previous game, there was a system of needs and fears. Here, it is replaced with a system of wants. Fulfilling a sim's want adds points to their Lifetime Happiness and mood. Some wants, like 'go for a walk in the park', add very little, while others, such as 'give birth to a son', can yield a thousand points. In the second version of the game, needs and fears also contributed points to Aspirations, which is akin to self-esteem. Positive moods can be gained from a delicious dinner or relaxing in a comfortable chair. Negative moods can be alleviated (for instance, if a Sim urgently needs to use the toilet) or corrected through socializing.
This version of the game also allows you to explore the entire world without long loading times and waiting. Each house is now time-synchronized with others: in previous series games, each house had its own day/night cycle. Players can interact with any building and objects in the city. Characters can enter stores, and players can somewhat limit but still manage characters within such 'public' spaces (schools, theaters, police stations, etc.). The player retains complete control over the sim when they are inside buildings like gyms, libraries, and beach houses.