Here's a pattern I've noticed: you either "don't get" Spelunky or you're obsessed with it. As a member of the latter category, I have the deepest sympathy for the former. I haven't played Derek Yu's masterful, procedurally generated platformer for a couple of months now, but I still think about it all the time, so news that Yu is writing a whole book on the game's creation is very welcome indeed.
Published by Boss Fight Books, 'Spelunky' is the "story of a game's creation as told by its creator", tracing its origins as a free PC game through to its rebirth as a multiplatform classic. Here's what the publisher writes:
"Spelunky is a game design manifesto in which Derek Yu uses his own game to discuss wide-ranging topics such as randomization, creative process, team dynamics, the philosophy of challenging games, and player feedback. Grab some ropes, a mattock, and your favorite pug—this book is going to dig deep."
Spelunky releases some time this summer (or winter down in Australia). You can pre-order it on the website, where you'll find several other books in the Boss Fight catalogue, including works on Baldur's Gate II, World of Warcraft, Chrono Trigger, ZZT, Galaga, Jagged Alliance 2, and Super Mario Bros. 2.