A semi open world, where you can walk next door, and visit, without a loading screen, but the game then loads the next section of the map, so you can go the next next house, and so on. You can always see the next part of the map from the lot you're on, with it loaded and ready for you to visit.
Many RPG type games work without loading screens, so why not the sims?
I'd also like to see more complex individuality for sims.
Not just walk style, but personal style for many other everyday things.
Eating style: Does your sim eat with their hands? Do they eat European style or American style? Chopsticks? Spoon?
Sitting style: How do they sit on a couch? How do they sit at the table?
Greeting style: How do they greet friends? Family? Strangers?
More personal likes and dislikes.
A bookworm will spend half the day reading, but a sim who hates books will struggle to read for an hour.
A sim who enjoys cooking will be happy to make a fancy meal, but one who hates cooking will be happier if they prepare a microwave dinner, rather than a fancy meal.
Multiple favourite food options, and multiple disliked food options.
The ability to create our own clothing categories, and then set them as a preference for each sim.
A companion program similar to bodyshop from TS2, but with the create a style from TS3, and be able to use it for not just clothing and accessories, but also for buy mode objects. And the objects should have multiple recolour channels. Eg, change the sofa frame colour, change the colour of the soft part of the sofa, change the colour of the decorative cushions on the sofa. Change the bed frame, change the sheet set, change the quilt.
More job options, many without much chance of progressing, as they're just a job, not a career.