It's hard to describe without seeing it in practice and knowing through playing it that it works. What I can vaguely say I think I want is, largely:
1) gameplay that is more interactive (not big on watching my sims do stuff)
2) autonomy/behavior that is more varied/distinct and maybe just in general, a bit less hyper. by that I mean, like, sims don't necessarily need to be jumping around doing something hyperactive constantly if they are simulating real life. real people are not on the move all the time. they do uninteresting human things like sit and think, get distracted, take their sweet time to get to something. And yet, some are more hyper than others and more restless in general. Having more of a range of behavior in this kind of way would probably go a long way in making sims more distinct.