I like the ghosts in the Sims 4, however, they're only really useful if you want to play as them and wouldn't be considered very scary at all. As far as I know, ghosts don't generally give your sims ...
I would love it, if we had random ghosts coming to the Sims house probably like... Once a week at night and haunt them (either going in the cupboards and wreck everything (making the house a mess), any sims that are up they scare.