The Sims 3 is built upon the same concept as its predecessors. Players control their own Sims' activities and relationships in a manner similar to real life. The gameplay is open-ended and indefinite. Sim houses and neighborhoods are placed on one continuous map. The developers stated that "What you do outside your home now matters as much as what you do within." One of the biggest changes to the franchise is the use of "rabbit-holes". Players aren't allowed to go inside the majority of city buildings; instead, the Sim will disappear inside for a certain amount of time—a feature known in video games as a "rabbit-hole"—while the player is given several choices on what happens inside using a text-based notification.
The Sims 2 used a reward system called Wants and Fears. This is replaced with a new system called Wishes in The Sims 3. Fulfilling a Sim's wish contributes to the Sim's Lifetime Happiness score and mood. Some wishes, such as "Go to the Park", may add little points to their lifetime happiness while a wish to "Have a Baby" may add thousands of points. In The Sims 2, Wants and Fears also contributed to a Sim's "Aspiration" meter, roughly analogous to current self-esteem. In The Sims 3, Aspiration is removed entirely, replaced with "Moodlets", which contribute positive, negative, or neutral values to the original Motivation meter. Moodlets can be inspired by physical events, such as having a good meal or comfort from sitting in a good chair, as well as emotional events like a first kiss or a break-up. Most moodlets last for a set duration, but some negative Moodlets can be cured and some positive ones rely on the Sim's surroundings and traits.
The game includes an optional feature called "Story Progression," which allows all Sims in the neighborhood to autonomously continue as if the player were controlling them, such as get married, get jobs and promotions, have children, move into their dream house or move out of the neighbourhood while the player isn't playing. Sims live for a set duration of time (adjustable by the player) and advance through several stages (baby, toddler, child, teen, young adult, adult, and elder).
Sims can die of old age or they can die prematurely from causes such as fire, starvation, drowning, electrocution, (as of the World Adventures expansion pack) Mummy's curse, (as of the Ambitions expansion pack) a meteor, and (as of the Late Night expansion pack) by thirst (vampires only). One of the major new additions to gameplay is Opportunities, tasks that Sims can complete to earn rewards. These challenges occur randomly based on aspects of each Sim's lifestyle, such as relationships, skills and job. Career opportunities such as working overtime or completing special tasks can yield a pay raise, cash bonus, or relationship boost. Skill opportunities are requests by neighbors or community members for Sims to solve problems using their acquired skills for cash or relationship rewards. If the opportunity is connected to a Sim's school, the reward may be increased school performance.
Sims can die of old age or they can die prematurely from causes such as fire, starvation, drowning, electrocution, (as of the World Adventures expansion pack) Mummy's curse, (as of the Ambitions expansion pack) a meteor, and (as of the Late Night expansion pack) by thirst (vampires only). One of the major new additions to gameplay is Opportunities, tasks that Sims can complete to earn rewards. These challenges occur randomly based on aspects of each Sim's lifestyle, such as relationships, skills and job. Career opportunities such as working overtime or completing special tasks can yield a pay raise, cash bonus, or relationship boost. Skill opportunities are requests by neighbors or community members for Sims to solve problems using their acquired skills for cash or relationship rewards. If the opportunity is connected to a Sim's school, the reward may be increased school performance.
Source: http://en.wikipedia.org/wiki/The_Sims_3