Andy has some video of some in-game developer commentaries that are included in the Half-Life 2: Episode One. They're a cross between a typical DVD director's commentary track, hyperlinked footnotes, and a first-person video tour. Fascinating.
Perhaps the coolest, though, is a commentary where they show how an in-game video projection--where a game character's talking head appears on an in-game monitor--is made. Turns out the clip is actually "shot" "live" in a walled off part of the game, and "broadcast" to the monitor. It's like in-game machinima or something, which is a bit to recursive for me. I think my head will explode.
Half Life Developers' Commentary [waxy.org]
