The biggest difference is that Sims 2 and 3 worlds are much bigger and more customizable than Sims 4 worlds. Plus Sims 3 neighborhoods could have some fun areas. Aside from the fact that you could swim in nearly all of them after an update, you had a variety of locations to visit (graveyards full of ghosts and rabbithole mausoleums off the top of my head. We also had more lot types than Sims 4, though a lot of them can be replicated in Sims 4 anyway.)
At the very least, if we're getting smaller worlds with much less customizability, they should at least make the worlds more interesting and fun.
