It was hard to pick three, but I know that doing just these alone would make the game so much more involved, entertaining, and overall more enjoyable:
Impactful gameplay. The most boring thing about TS4 is how it feels like nothing is ever happening in the world. There's no consequences, and the things we have our sims do have no impact on what happens to the world and sometimes no influence on the household itself.
More diverse personalities. Traits are my least favorite thing added these last two games, and they make the sims themselves seem extremely shallow and no different from each other. Sure, visually we can make completely different sims but it doesn't matter if everyone reacts to things the same way. If you don't plan on ditching this system, at least make the traits do something more than giving them moodlets and different idles.
More control over everything. Please, stop making everything under "your vision". It really limits the game's replay value when we can only play the game ONE way. Your way. Whatever happened to the tagline "You Rule"? If you ask me it has become less, and less true the further we get into this series.
Simulations are meant to simulate things. Obviously. A simulation is less interesting if all characters behave the same way, nothing happens in the world, and we have no way of shaping the world on a deeper level. If it weren't for mods like MC Command Center, I would probably have left this game on the shelf a LONG time ago. My favorite packs so far have been Vampires & Parenthood, because our choices did matter.
