I know there are some issues with the world and simulation, but mostly, I miss the open world.
I liked seeing the neighbors going about their lives; it made the world feel more real and alive. In TS4, the same group of sims walks through the neighborhood on a constant loop. Even the sims who live in the houses next door walk by in a loop, since they can't interact with their own lot at all.
Although I kind of like being able to get to a different world if I want, it feels like it's come at the expense of lot amounts in any given world. For some players, they can use lots anywhere, but for me it's completely immersion-breaking for my sims who live in Strangerville to have to go to a gym in Willow Creek and a restaurant in San Myshuno. And then you see the same sims pop up in Sulani and Forgotten Hollow and Oasis Springs.
I would be much happier with the closed neighborhood system if they released a world builder tool that let me create one big world with more lots in it.
