It is a little embarrassing to even have to name a few very basic things for this: Elevators, spiral staircases, cars, pool tables.
Why are those four things STILL not in yet after so many expansions? Especially with how annoying stairwells are in Sims 4, I would be very happy to just have an elevator or spiral staircase option to make that a lot easier.
Outside of this, I would mainly say animations. Sims 4 is notably devoid of a lot of animations, a trend that was already started in Sims 3. Both Sims 1 and 2 have animations for a lot of interactions that sims 4 has none for. Again, something pretty embarrassing since these games are decades older.
I also miss the occult stuff. It's wild that Sims 4 still manages to be pretty boring despite having way more expansions than previous sims games. It's just giving a lot less actually new things in each expansion. Like businesses and hobbies offered us just ONE hobby: Pottery. Sims 2 offered like a dozen hobbies with their hobby pack.
I'd like sims 3's more meaningful alchemy potions to return. Most in sims 4 are worthless, just giving some meaningless emotional moodlet. Not turning someone into a specific occult or such, or curing them of that. No spell to turn someone into toads either. Heck there's still nothing for male mages to wear in sims 4. No pointy hats, no proper mage robes.
They seriously need to release a full expansion dedicated completely to the occult stuff, Life and death was the first of like 20 expansions to have SOME occult stuff in there but still very little. I want to see it be the full focus of an expansion, like it was with Sims 3's supernatural. That's still one of the best sims expansions around. Sims 1's making magic too. Both have a lot of things I'd want to see in sims 4.
