Sim houses and neighborhoods will be entirely in one continuous map, and the developers state that "What you do outside your home now matters as much as what you do within." All the Sims in the neighborhoods age and live out their lives simultaneously, no matter where the player is in the game.

Of the eight needs of The Sims 1 & 2, only six—hunger, bladder, energy, social, hygiene, and fun—remain (removing comfort and environment). These will be represented by moodlets—attributes which are acquired special events, such as minor events like tooth brushing and major ones like a wedding, and affect the Sims' behavior. The needs will also have only 3 stages—red (extremely low), yellow (moderate) and green (completely full.) Several minor features from The Sims 2 expansion packs appear in the original The Sims 3, such as the "young adult" life stage and mobile phones (University). Private cars, personal inventories and restaurants (Nightlife), fishing and gardening (Seasons), jewelry and beaches (Bon Voyage), toothbrushing and ceilings (Apartment Life)will be included, but none of the main features from expansion packs such as a sim going to college (University) will be available yet.

As in previous games, Sims can paint, but paintings will now be more unique to each Sim based on their traits. Other new features are set difficulty levels for each family. There are also hospitals where pregnant Sims may give birth, and bicycles for riding around the neighborhood.