You know, if it hadn't been for Athkatla in BG2, I would have had pretty much zero interest in the game. I didn't care enormously for the story, there weren't many interesting choices to make. But Ahtkatla. Exploring Athkatla was enormously fun. And it showcased that, maybe, just maybe, an isometric game that "abstracts" a lot of its world is the best way to bring a city to life in an RPG. It had character (it almost *was* a character), it was atmospheric, it was dense, it was occasionally dangerous.
The same goes for Sigil in Planescape: Torment of course. How exciting it was to explore just what lies in the city's various districts. How awesome was it to leave the slummier and dirtier Hive Wards and Lower Wards behind and find out that, yes... There is another goddamn district waiting to be explored in the Clerk's Ward, this one with a completely different flavor.
Basically, Athkatla and Sigil were a really big part of BG2 and Torment. A lot of the games revolved around those locations, and it didn't feel like the games sold the idea of a big city short. They felt big and lively.
Now, including such big areas in a game is obviously not an idea to be taken lightly. Would you like for there to be a big city in the game which "dominates" much of the gameplay? Would you rather have more, medium-sized settlements (that may differ more culturally speaking) to explore?
I wouldn't be disappointed if we got smaller settlements. But I *would* definitely love a big city that you can really dive into.