I think the main priority improvements I'd want are:
- Option to turn off the mobile phones completely. No autonomous use, no calls, no texts, no unwanted invasion of random townies trying to contact my Sims just because they were in the same place at the same time once. Just the ability to stop the madness.
- World editing tool. I want to customize my neighborhoods the way we could in the other games. Even if it just meant basic object placement areas, I really really want to get rid of all the excessive playgrounds and barbecue picnic areas and put something interesting there instead that I would actually use. Or I'd just fill them with gravestones. But it's a huge downgrade that we can't change anything at all in the neighborhoods.
- More Sim tuning with reactions and animations. This would cover a bunch of things, but mainly, further tuning to make Sims more reactionary to their traits, likes and dislikes, preferences, quirks, reputations, etc. Also, instead of all Sims having the same default reactions to the same things, like decorations, radios, computers, etc... have them behave according to their own personalities. Materialistic? Then sure, react to the nice decorations. Foodie? Then sure, be happy when you have a nice meal. But others without the appropriate traits? Not so much. This would also require autonomy tweaks as well. Autonomous behavior should also match a Sim's personality. If a Sim hates children, why would they autonomously try to care for an infant? If a Sim is mean, why would they hug someone after a fight or pretend it never happened? They should mock them instead. It all needs to make sense. And maybe it would help if object appeal was turned down in general so that Sims gravitate more to each other rather than objects. But not if they are Loners, of course. Also, we need new conversation animations. The current ones are so tediously repetitive.