The Sims 4, and the slogan for this iteration is "Mind. Body. Heart."
The UI will be far sleeker, with fewer buttons and a minimalist interface. For instance, individual Sims seem to have a single floating notification, showing their emotional state. (It remains to be seen if the UI is adjustable. It could be the status bars were toggled off to make the presentation more cinematic.)
Home creation and Sim customization has been made far more intuitive. Rooms can be stretched and sized, and in the case of second floors, merely dropped onto the first floor. Gamers can finally cut-and-paste rooms, as well as have pre-furnished rooms.
Similarly, Sim creation is more intuitive, as gamers can literally stretch and pull at Sims. Some of the Sims created have more extreme body shapes (that is, really fat or rail-thin), something players have been pulling for. Sims will also have individual walking styles as well.
One of the bigger updates is the emotional states of Sims, who will be defined by their mood. Happy, sad, angry, romantic, all of these moods affect a Sims' behavior and actions. Sad and angry Sims can't romance, but they can paint and swing at punching bags to blow off steam, respectively.
The emotions can be manipulated in several ways. Sim objects like violins can play a sad song to make a Sim sadder. A Voodoo doll can make them angry, while decorations, paint and furniture can influence emotional states as well - a particularly phallic painting of a girl riding a rocket can make a Sim more... romantic.
The Sims 4 will be released on PC in 2014, and will be, as EA stresses, a single-player offline experience.