I was never a fan of the open world in sims 3. As soon as my family had more than one member, they could be scattered across the map and I found it a pain to zoom across the map between sims. And I couldn't ignore the sims at home because they remained active 24/7. Besides, I found the open worlds to be closed at the same time because they were self contained. Most packs brought its own world which was completely separate from the existing ones. you had to start a new save to explore the world of a new pack (or move your existing sims and cut ties with all their friends and extended families)
For sims 4, it would have been nice to have open neighbourhood. It could be an open environment on a smaller scale with the option to travel to other neighbourhoods. A loading screen to load the lot across the street is annoying.