Intimacy between sims. S4 couples act more like friends than lovers. 3 bolts sims will autonomously leap into the arms of their partners whenever they want, do incessant romantic gestures and are generally inseparable, the way they cuddle on beds and couches (my favorite is when one Sims wakes up and cuddles with the sleeping Sims, now that's the kind of detail S4 needs more of).
S2 sims react to their surroundings, I can tell whether they like/dislike, are sad, happy or angry at something by watching their reactions rather than colorful moodlets and music. Sims who cook a lot will rub their belly from time to time while thinking about food.
The cut scenes of important life events. both the goods and the bads.
Businesses.
Sims 4 is closer to an RPG game than S2, I like figuring out what to do to make sims Sims happy (or not) in S2. Sims 2 is about the Sims themselves, the family and the relationships between them which is not as much the focus in S4, unfortunately.
The personality actually matters in this one and if I order them to do something that goes against their established personality, they'll let me know.
