Added Sep 13, 2012.
I had this book for years, and I've read through it many times. It's helped me be a better game designer, and helped me think critically about decisions I make for our studio. When PAX East 2011 came around, Valve had a Portal 2 booth on the show floor. I took the opportunity to ask Erik Wolpaw and Jay Pinkerton to sign the book; though it is not a Portal art book, it embodies the same design philosophy underlying Portal and Portal 2.