Favorite animation
For the longest time I'd named the hottub woohoo here, because it is adorable, but there's one that is so useful that it beats cute: Sitting on the ground.
Sims being able to sit on the ground while also talking to each other as well as to sims sitting nearby is such a godsend! The sim pictured here, Poe, is talking to his droid - ingame he uses the "Practise singing" animation. It looked so natural, especially with the little guy turning his head occasionally.
(The droid is a regular JtB droid, only with an orange recolor.)
Poe, sitting on the ground, discussing plans with Commander Trach.
Of course I could have had the same conversation with both of them on the couch, and the effect would have been the same: Their relationship would have risen. But the ground-sitting animation makes the scene so much better visually, contrasting the more casual Poe with the proper officer.
What are your favorite animations? Anything that changed your game on some fundamental level?