A handful of years ago, Geoff Keighley wrote of his first-hand experience inside the halls of Valve Software as the finishing touches were being put on "Half-Life 2." The piece, titled "The Final Hours of Half-Life 2," is a fascinating look into a company which has, traditionally, dodged the media spotlight. Keighley has since gone on to do a number of other things, including being the host of GameTrailers TV, but he apparently hasn't forgotten his roots or the familiar folks at Valve. Keighley returned to the company this year for a new feature, "The Final Hours of Portal 2," in which he documents the process of creating what I would consider to be one of the best games ever made.
Unlike his "Half-Life 2" feature, "The Final Hours of Portal 2" isn't available for free on the web. Instead, it's being sold on the iPad App Store for $2, available only to those with Apple's tablet.
The feature is a mix of text and multimedia, with details on some of the major changes in "Portal 2," including its origins as a prototype called "F-Stop." There are even some amusing minigames tossed in to show some of the title's features, such as the degradation of the test chambers and how portals are designed in the game.
Obviously it's strongly recommended that you play through "Portal 2" first before giving the feature a read. While it's relatively light on spoilers, you probably won't understand many of the references until you've completed the game. The same goes for the in-game commentary track, which is free with all copies of "Portal 2."