This article (in older forms) has been floating around for a very, very long time on Dave Johnston's website. I remember it inspiring me to work harder on my own attempts at level design but also that there's a top tier skill (and level of commitment) that I eventually realized to never reach. It's mind-boggling to see how many considerations go into making a great (not good, great) map, even in much simpler times before true photorealism. Yet even then you can never predict how well it will work out in the end. It's a really interesting discipline between game design, architecture and understanding the technical details of the underlying engine.