As for the Sim's personality, it's now based on a choice of traits that will definitely affect the way your Sim behaves, reacts and lives. There are also more customization options for clothes and furniture, to which you can add your personal touch with colors and patterns.
The Sim editor has been greatly improved and now enables you to customize your Sims to the smallest detail – like defining the length of their eyelashes. There are also more options for socializing, and for the first time, you get feedback in real time about what the other Sim is thinking about you.
If you've been following the saga, you'll immediately notice tons of changes and new features in The Sims 3: the first and most important one is probably the fact that you can now get out of your home and visit not only public spaces and community buildings, but also other Sims' houses – and enter them! This freedom of movement in The Sims 3 makes it easier for you to find a job and make new friends in the neighborhood.