1) The streets look so bare, there don't seem to be any trees along the sidewalks! Trees lining the streets clearly seems to make a big difference in how the city looks. I can't imagine how unnatural and impersonal the place must have felt before all the trees were put in.
2) How quickly the city seems to taper off into comparative nothingness. Old photos of the NYC outer boroughs and the outer parts of Boston make it seem like the "suburbs" consisted of farmland, with random-seeming pockets of mansions and other urban buildings scattered throughout. I don't know how true that is, but it's a weird thing to imagine. It's amazing to think that anyone had the foresight to run subway lines out into these areas, which at least in photos seem very rural and almost desolate. Nowadays, I am used to the idea that cities generally have large dense "metro areas", which gradually taper off with decreasing density as you move further from the center. Some cities are exceptions to this, e.g. the city of Rochester, NY, which kind of just "ends" at its western border (the Erie Canal), rapidly dissipating into rural suburbs of Gates, Greece, and Chili. But this always seemed like a strange and jarring transition to me. Maybe a lot of places are like this? And maybe more places were like this in the past.