I think that it's a common misconception that TS3 base game restaurants weren't "open". Actually, they were. There was always the option to choose to eat outside.
I loved doing that when the weather in-game was good. My Sims would eat outside and NPC would be out there as well. There would be lots of meeting and greeting going on, no different than the open restaurants in TS4.
There was a really nice lot that I downloaded from the Exchange that made use of the restaurant rabbit hole that looked like a ship. Because I could place lots wherever I wanted, I placed that restaurant lot half in, half out of the surf. With a little terrain editing (because that was an awesome thing), Sims on that lot were able to eat in the surf, just like you would see in upscale resorts IRL. They sat at the tables with water lapping at their feet. :) It was incredible and a favorite place for sending Sims on dates.
For me, that was the beauty of the open world -- the ability to put lots exactly where I wanted and to build incredible things that I will never be able to build in TS4 because the game doesn't allow anything creative like that. Lots exist only where they allow and they are all perfectly flat. I preferred an open world with extensive terrain tools. If it wasn't for the fact that TS3 still has a 32-bit .exe (which is part of the problem of games crashing under the weight of all of the content), I wouldn't have looked at TS4 twice.
When I choose to actually play (as opposed to setting up scenes which is all that I feel that I can do in TS4), an open world will always be my first choice. An open world with a 64-bit .exe, the sky (and your available memory) would be the limit!