There are still many things I would change, but for the sake of this thread, I will name two. They're probably difficult changes, I know the second one is for sure, but the heart wants what it wants.
1. Neighborhood editing tool.
I don't necessarily need a world creator (though that would be rad) but I always feel like I need a way to edit the existing worlds in some way. This is probably one of the worst decisions made for Sims 4 - to exclude neighborhood editing for players. It's such a staple feature of previous Sims games that it's like the elephant in the room...or rather...the missing elephant from the safari. With all of the constant complaints from players about how boring most of the worlds are, it would make a huge difference if we could set up our own common world assets. Even if it was just select areas, like the playgrounds and picnic areas, or where existing objects are placed. To be able to swap out objects, remove public toilets, change playgrounds into graveyards, place a weather changing machine or nefarious wishing well, design public gardens, arboretums, etc, etc... this would change the game for everyone, both players and builders alike. It would be especially awesome if we could swap out building shells and had access to the ones that exist from all the packs so we could pick and choose how urban or rural our neighborhoods are.
I'm pretty sure this is the feature that I want the most right now (besides more Occults).
2. Alternate "failure" programming.
I still have issues with the game being too Utopian and I really dislike feeling like EA is dictating to me how I should be playing my own Sims game. The entire reason I fell in love with Sims 2 and never got bored is because of the risk factor. In almost every choice, there was a possibility of failure. With every positive outcome, there was a possibility of a negative one. You didn't have to put extra effort in to have Sim enemies or meltdowns or even death. It was something that would happen on its own if you didn't manage your Sims on a path to success. So I would want more risk and consequences added into some Traits and social interactions. If my Sim picks a fight with another Sim, I don't want them to smile at each other when it's over and hug goodbye (true story, this actually happened to my Sim, it was ludicrous). I'm not saying that the game should have total carnage, or even risk to the extent of the previous games, but something. I want to be able to have stories where my Sim doesn't always succeed and has to find alternate ways to beat the odds. I want stories of relationship failures and struggles. I want stories of anxiety and distress. Without obstacles for my Sims to overcome, how can I say that they've really succeeded? When accomplishments require no effort, how can I call these stories "meaningful"? I feel like there's a stigma with this game that disallows for hardships and human error. But those things are also a part of life and many people relate to that. Why are they treated like taboo? People who have had to conquer such situations in real life have no representation and no way to tell their own stories. Failure should not be anathema in a life simulation game, but it's so rare. The previous games used a comedic approach that was genius. So if I could choose, I'd put more of this back into the current game to make it more stimulating. Maybe I wouldn't fall asleep at my keyboard sometimes when I try to play. :p