I've been toying with some Portal 2 designs. These are some screenshots of one area (BTS); this area is only a small part of what will be something much larger.
http://puu.sh/kohnN/409dcef3b9.jpg
http://puu.sh/kohp9/024d5bb2f5.jpg
http://puu.sh/kohlx/46bc21a62f.jpg
http://puu.sh/koio8/c2419b19cd.jpg
http://puu.sh/koiye/d2a5bbdc6f.jpg
Again, still experimenting with things.
Feedback (including any criticism) is appreciated!

I watched your video on BTS aesthetics before I started designing, so that helped a lot. The 2nd screenshot is meant to be dark, as it's supposed to be a "the lights died" scene or whatever you'd call it. I do agree that the whole place is a little too dark, though.