1. Natural lighting. I generally do not need artificial lights in the daytime in any room and it is amazing.
2. Ceiling height. Modern constructions have insanely high ceilings. Why? In my old apartment I had cabinetr y I couldn't reach even with my step ladder.
3. Old neighborhoods are much more pleasant to live in and are more much walk-able than post-war cul-de-sac filled developments.
4. House sizes were smaller back then. Since family sizes have been getting smaller I think this would be a good thing to return to. I am quite happy that I don't have to spend a lot extra on furniture just to fill the space. Or pay more to climate control the extra volume.
5. A matter of personal preference but I think the older houses are just prettier.
I think it would be great if developers took a look at the older house designs and tweaked them for the modern world.