Though, to your point, I don't want to have a large map, for the sake of having a large map, if there's really nothing to do while you're roaming around, and particularly, if everything looks the same (I'm looking at you, Saints Row 3.)
The funny thing is, SR3's map was actually much smaller even than SR2... and it was just a lifeless homogenous pile of crap. DR2 was a little flat, but christ that city felt alive and vibrant, more than any city in any video game I have ever played. But the size of the map was in fact still too small, it was JUST city... City and Water... there was really no contrast, no sense of connection to anything outside the city.
Sand Andreas had the best map of any video game I have ever played, tied with RDR. Both maps were diverse and offered more than just a static environment.
Now Night City, it has to be bloody huge... sprawling and immense. With zones as different from each other as night and day. Their has to be contrst and dochotomy. And part of that is giving us a look outside the city, at the abandoned rural atmosphere. The corporate Zone represents the Pinnacle of success. Everything is clean, the people are sculpted and attractive, and wealthy. The buildings new and gleaming. The moderate Zones are where the normal people shop and work and live, large apartment buildings and brownstones. Maybe even the occasional neighborhood of houses. Afterwards you get into the ghetto, where everyone is hungry, the streets are filthy, and life is hard. Then you have the Combat Zone.... the buildings are crumbling and falling apart, the streets are broken and full of burnt out vehicles, the gangs will kill you for the pack of gum in your pocket. And finally you have the wasteland, where people are poor, but live free, perhaps the only truly free people in Cyberpunk America. They have nothing but what they can carry on their backs, and every day is a struggle, but the only thing they have to answer to is the siren call of the road.
These aspects must be shown, they must be felt. The contrast has to be there. If it's just the city, then it really isn't any different from a thousand games before it.
To paraphrase Neil Gaiman "What purpose does hell serve if it's inhabitants cannot hope to see heaven?"