Now I wouldn't go as far as saying that nothing at all needs to be fixed, but this comes closest to how I feel about this issue.
Musical Chairs and the constant sitting down during conversations, for example, are/were a big problem for me. At them moment I have a mod to deal with it, but the next big patch is already around the corner, so we all know what will happen to it :'(
But I always was and am still fine with the core, because several of the big problems just do not come up in my game. I'm too much of a micromanager to wish for independent sims personalities or moveable babies. Even simulation lag takes a long time to rear its ugly head in a no-autonomy game.