apart of everything that's been mentioned already:
- hair physics (would be cool to have clothes physics as well)
- relaxing, reading a book, daydreaming, etc on the bed
- lounging on the sofa
- pretty much more interaction with the world they're in like sims 2. the most popular example being how in ts2 sims do actually use the counters instead of magically making appear things on their hands. these kind of details may be useless for some but sometimes i just loved doing nothing, watching my sim doing their things alone and be amused at they way they would do so.
- that little window that popped in the bottom right corner when another sim was heading to the house door. it was rather fun seeing the grim reaper walking to the door to pick up my dead sim lol.
- being able to go shopping to get new clothes & food
- when you clicked for an interaction the selected sim's face would appear in the middle of the menu. i liked it.
etc
someone mentioned onlyabidoang sims 1, 2&3 details videos, i recommend them as well :)
