One of the benefits of working on HL1-based maps was that it took an order of magnitude less effort and less detail to create an area. Case in point, all of Dust was basically created from two brushes that were duplicated over and over and then tweaked into position (these were the surrounding walls with the trim at the top.) The roofs all over Cobble were the same. With Dust 2, I was even cheekier and copied Dust 1.
The big problem with this approach is that - as quick and easy as it is - the cookie-cutter approach makes everything very repetitive. Take it too far and two distinct areas look identical.
On the other hand, some maps have had every brush individually carved and placed, but suffer the same problem - they’re so uniform and boring. This happened a lot a few years ago in the CS scene when everyone tried to up each other on polycounts and ‘neatness’; maps ended up dull, repetitive and lifeless, but the skill put into achieving it was top-notch. Very well done.
Sienna was also copy’n’pasted. Lots of it. However, every section in Sienna was redesigned a couple of times, buildings were retextured, re-adjusted and changed to prevent this exact problem. That’s why it has three very distinct sections, and this was accentuated when Valve gave it an art pass. Variation made it look more lively, and hence it’s often easier to navigate since areas are distinctive.
With Source, these problems become even more apparent. Real life is not repetitive. The original Dust - in source - would look horribly plain. These days I’ve got into the habit of looking for large patches of nothingness and work out how to break it up. Skylines need not be straight. Edges should not be tidy, not always.
Copying and pasting is not a bad thing (shift-dragging is my main tool) but overuse of it is, and a very bad habit to let get the better of you. Everything you ever create in a map, always give it at least three glances before you stick with it. Chances are, you’ll change your mind or find something better.