your point for gta is perfectly valid, but not sure where your going with the imperial city as you could interact with everyone and enter ever building. The filler npcs in oblivion actually had more to say in comparison to the filler npcs in skyrim as well. The houses were cookie cutter though (so were alot of morrowinds). I'd also point out that the imperial city had it's sewers under it which served as a large ruin/ dungeon so the city's space wasn't too badly used. Anyway what I'm trying to get at is that a larger city doesn't necessary mean that it's going to be more boring, it all comes down to how much effort they put into it.