I don't know about you others, but to complicated for me
Just haveing a couple of different walls like the ones described in the list is good enough for me.
Also in modern times there are limited use for city walls. There should instead be several "replacements":
-A bonus for infantry defending against armor inside the city.
- You should be able to entrench (is that the right word?) units around your city.
- Build bunkers and fixed guns.