I read through 96% of the article. Itook notes for the general sense, but here's notes that can apply to TF2:
+ when designing the level, think of the environment. What is the geology? Geography? Topology? Climate? Age?
+ integrate the landscape into your architecture
+ include time when designing your environment. I feel that this is something that many of don't think of when detailing, or making new geometry for levels
+ how does the levels landscape evolve through time? What did the landscape look like when the buildings/complex was new? What's the landscape going to do to it now, X years later?
+ what do buildings look like through time? How would they be repaired. How would the materials of the new repair compare to the old materials?
+ in the case of tf2, what are buildings in similar environments built like? If the area could be prone to flooding, your buildings should reflect this.
+ consider how materials interact. What do they look like new? What do they look like aged? What do they look like together? You don't want to have that stains on a building that doesn't have a source of rust.
+ be consistent! Again, think about time and age.
I guess the biggest thing to take away from this is: include time as an aesthetic part of your environment. Time will effect every aspect of your level and environment, don't forget it!
On mobile, so formatting is poop.