Here's what my perfect Sims game would need to have.
Life stages: Newborn (self explanatory, not much activity), Infant (Up to 9 months, starting to crawl maybe even waddling around a bit), Toddler (around 2, can walk and start learning to talk), Child (6-7, Very hyper and playful), Pre-teen (10-12, calmer than the child, more into hanging with friends), Teen (15-17, getting first part time job, hanging with friends after school, learning to drive), Young Adult (20s, going to university and getting full time jobs), Adult (30-40, same as young adult, but loses stamina more quickly), Elder (65+, retirement).
Equal (or near equal) CAS for all age groups. This includes customization for babies.
Good AI, meaning Sims wouldn't autonomously do stupid stuff. EX: Married straight Sims wouldn't flirt with random other sims of the same gender (unless there was some sort of trait that would cause this).
Large amount of traits and aspirations that are different for each age group. Likes and dislikes, fears, favorites, etc, more things like that to influence their personalities.
Lots of job options.
Diverse neighborhoods and NPC families. I want peaceful suburbs, busy cities, quiet countryside, etc. And idk about past iterations, but TS4 families are boring and basic. Give me a family with 2 parents and 6 kids of ranging ages! Or a single parent with 7 kids! I want more than just mom, dad, kid or 3 roommates.