My big 3 are:
-emotions/traits and how they work (or don't work).
-Anything phone. Just UGH. They call and text at weird times and for weird reasons. Travelling by phone is also really strange. It's like each sim has a free personal taxi service. That said, the phone UI is a huge improvement on S3 for me.
- Autonomous anything. I'm all for autonomy but it seems pretty broken atm, and I can't leave my sim alone. Sims drink water instead of taking a shower, take out garbage instead of getting food, wash dishes in the bathroom instead of at sink, and play phone games in public when their social needs are low.