Rule number 1: Do not add in any outfits that randomly overwrite the clothing chosen by the player (or by the filter template of a random sim).
Festival outfits, vampire walk-by outfits, rain outfits, towels with a ridiculous amount of add-on accessories (why do they need any at all?), party outfits...the list goes on and on. Since they are all random most look plum plumbity plumish, and more importantly, they take away from whatever the player has chosen to do in THEIR game. Everyone hates these "situational" clothes, and the only exception to the rule should be costumes for holidays (like Halloween, and I can even bear them at the Geek festival). But if I create a bohemian island girl, she doesn't suddenly need to dress in a turban, elbow length leather gloves, an orange visor, flowered tights, a Moschino sweat shirt, etc, etc, etc, because there's a party in the air. It's a party, not weaponized lsd. Every pack that comes out seems to add more situation outfits in, and it's so irritating.
And by the way, turbans and the like should never have been cold or hot weather clothing by default, so any sim (especially Mortimer, who's obsessed with them) can end up wearing them. I see three times as many sims with turbans for winter than stocking hats (At least I did until I nuked them). Because any sim CAN wear them, if you go into cas and CHOOSE them.
Rule number 2: Player chosen actions should rule.
Almost all actions chosen by the player should outweigh those pressing in by other sims (or by the player's sim, or by anything else). If I queue up (clickity-clickity-clickity-click thru the menus) three actions for my sim to do, they shouldn't suddenly cancel out because my sim has two celebrity stars and a fan wants to talk to him. It should appear in his queue after my actions, allowing him to talk to him if he chooses. Sorry, Stan, but that's how life works. If Brad Pitt is on his way to the boy's room, he's not going to stop because some random person wants him to unless he wants to, but maybe on his way back out). Or if a dog wants something. Or someone wants a random hug. Or any other of the fifty random reasons my queue drops out, now. I'd estimate I lose about 25-50 percent of my actions now if any other sims are around. Again, it's the PLAYER'S game...we're the one playing it, not the flippin' computer. Let our actions choose the flow of the game. It's endlessly frustrating having to re-queue actions again and again and again. And for Pete's sake, put a distance limit on Sims choosing to come and talk to another sim across a neighborhood. Same thing, they suddenly show up in the queue, all actions stop, you have no idea where the sim even is, and it always fails because they are a half hour walk away.
Rule number 3: Design all items you put in the game to be used anywhere.
There's nothing more frustrating (except for maybe rules 1 and 2) than looking forward to a new item of some kind, then being disappointed because it only functions right on certain lots. Like the food shacks. Without mods, they only work where YOU put them. Why? Why can't every sim worker tended object, such as a bar, a market stall, or a barista bar, work on any commercial lot? If I want a fish sandwich joint outside my nightclub, why can't I have one? Or a snack shop on the patio behind a gym? Because it does work, I've modded it myself, as have others. So why can't you have it work that way out of the digital box? You have gotten better at making some other objects work in places they didn't before (the skating rink, karaoke, etc). But everything should be usable however and wherever we see fit. We paid for it, it doesn't mess up the game, let the player use all their resources the way they want to.
All these rules are related, and they point to the biggest flaw (imo) of the Sims 4; restrictions. The game constantly overwrites our clothing choices and chosen actions, tells us no to our ideas of what to build and where, and barrages us with things we didn't ask for. Like the never ending army of random sims, created just so they can walk by our house in a pizza outfit. No option to choose what sims are used for random jobs to limit their numbers, no way to create a pool of sims to fill those jobs, nothing (which would be rule number 4). I mod for my own use intensively, and it's exhausting at times trying get the game to play the way I want to. I spend almost as much time in Sims Studio as I do in the actual Sims, because some new irritation is always rearing its head.
The game has improved much over the years of its existence, but you keep breaking all the above rules again and again with every new pack. People post complaints about these issues over and over on the forums, and you continually ignore them. It's like you don't want the game to be liked, and are more wrapped up in shoving your own framework to play in down everyone's throats. You'd think after all the money people have spent on expansions and the loyalty they showed over the lean years you might choose to listen to them, but you sure don't seem to.