You already know about ghosts and mersims, so I'll stick to the others. Vampires (Vampires pack): very well developed. They come with a skill tree to build their special powers, but if you get a certain number of powers, you have to pick a weakness. This makes them more balanced and less op. Energy and hunger work differently for them, and they are immortal. Strongly recommend this pack to anyone who enjoys playing with occults.
Werewolves (Werewolves pack): Also have a skill tree and they also have weaknesses (called temperaments). For werewolves you don't get to pick their temperaments, although one of the special powers you can pick for them allows them to re-roll their temperaments. They aren't necessarily immortal, but you can pick immortality as a special power. They are subject to something called rage that, if it overflows, can cause them to go on a rampage where you only have limited control over them. The werewolf world, Moonwood Mill, has a ton of lore to explore. Also recommend this for occult players.
Aliens (Get to Work): In my opinion, these are the flimsiest occult in the sims 4. They have a special alien form and they have some limited special powers. I do not recommend Get to Work for occult players who have no interest in the careers that come with this pack.