First of all, focus on the Sims themselves. It's THE SIMS; not Party Life simulator. Give them realistic personalities, extensive traits (at least five slots for adults), likes/dislikes, turn ons/turn offs, etc; as well as a decent attraction system. Just as important--I Do Not Want Online Multiplayer!!! That being a major factor in the early stages of TS4 is a main factor in its many problems.
Life stages the same as TS4; but make the Sim models more represent their age; and do them properly.
Decent Sim model that doesn't look like a cartoon character.
A small "town" area built like TS3's. That would include a grocery store, book store, police station, fire station, hospital, graveyard; as well as restaurants.
Improved CAS and Build/Buy, map editor/builder (which both TS2 and 3 offer) as well as the color wheel. The color wheel is important, because with many CAS items, the swatches or limited; and don't offer much creativity.
Cars are base game in TS3, but not TS2. I don't know if they should be basegame in TS5 or not. However, I think TS2 implemented cars best. If Sims teleport, they shouldn't disappear--they should be shown getting into a taxi/carpool when they leave and getting out of one when they arrive where they're supposed to.
I think neighborhoods should be open world, but not entire maps. That's just torture on anything that isn't a high-end performance gaming machine in terms of TS3.
Occults, nightclubs, bars, pets, anything else--save it for later EPs. I do not get why bars and lounges are basegame in TS4, but not in any other game; and were usually bundled with "Nightlife" type packs.
