They have never done ghosts right I feel. Not in sims 2 and 3 either. 3 did them the best probably, but they just aren't very fun to play.
In 4 they keep breaking things too, I just want to get rid of them when I have a ghost.
Just once, they should actually put as much thought into ghosts as in other super naturals, there's a lot of potential there. And sadly like in many things, Sims 4 is a downgrade instead of an upgrade over past instalments. If it wasn't the only sims game that's actually technically stable, it would not be played much.
A few things I think they could do with ghosts if they ever put them in a game again:
-They can't leave the location they died, they haunt it. Happiness/satisfaction could have a reward that lets them move around freely.
-They sleep in their grave or urn by day, and only are around at night. A happiness/satisfaction reward could let them be around by day too.
-They can be invisible.
-They get unique interactions as a ghost.
-Each of their traits has an effect as a ghost, enabling at least one extra interaction or a passive lot trait.
For example, a neat ghost would keep the place tidy. Anything dirty automatically becomes clean the moment the ghost wakes up.
A handy ghost would do the same with broken things, nothing will ever be broken while they are awake, it automatically repairs itself instantly.
A prankster ghost would pull harmless pranks around the house, moving stuff around like instruments or such.
A mean ghost could play meaner pranks, breaking things.
An evil ghost could be a real terror to any sim who is not a friend, not letting them sleep, spoiling their food, breaking things a sim is using, and they could even be the death of a sim in indirect ways. Like scaring a sim who is already very scared so they die of fright.
A vain ghost could constantly be seen in mirrors, your sims never get to see their own reflection. But can speak with the ghost through the mirror.
A family person ghost could look after children and maybe even play with them, like at a doll house making the figures move.
A clumsy ghost could be always breaking things.
A musically inclined ghost could have anything that plays music playing their favourite music all the time they are awake.
A lazy ghost could sleep more, being awake only a few hours at night.
A glutton ghost would always be raiding the fridge even though ghosts don't need to eat.
A natural cook ghost could have a breakfast ready for the household by the morning before they go back to sleep, and dinner ready when they wake up right after dark.
A loner ghost could actively avoid any interaction with the living, getting uncomfortable around them.
A snob ghost could destroy low quality objects to encourage their replacement with something better.
A daredevil ghost could enjoy playing around with Sims, like playing airplane with a child or causing big waves in a pool.
A jealous ghost could strongly attach themselves to one living sim and do mean things to whoever spends time with that sim who is not their friend.
A childish ghost could enjoy possessing stuffed animals and making them do stuff (which would no doubt entertain child sims.)
Stuff like that, there's so many possibilities to make ghosts fun.