I see in the comments that he has been working on a Quake Black Book, but I hope he plans to eventually do books on other types of games as well, instead of just Carmack/Romero-centric, raycasted first-person games. Don't get me wrong, I'd love to see a Commander Keen Black Book, but I'd also love to see a Morrowind Black Book or a Secret of Mana Black Book. The series could be really cool if he delved into other game engines and game mechanics.