Fabien Sanglard has written an interesting drill down into the recently released source code for Doom3. He tries to reason why certain things are the way they are and also had a few of his questions answered by John Carmack himself.
There was news about the source code for the Prince of Persia game on Apple II computers restored from a set of ancient floppy disks. There is also a great quote on why going through the trouble of restoring/releasing the source code of those games is something worthwhile.
“Because if we didn’t, it might have disappeared forever.”
Video game source code is a bit like the sheet music to a piano sonata that’s already been performed and recorded. One might reasonably ask: If you have the recording, what do you need the sheet music for?
You don’t, if all you want is to listen and enjoy the music. But to a pianist performing the piece, or a composer who wants to study it or arrange it for different instruments, the original score is valuable.
It’s possible, up to a point, to reverse-engineer new source code from a published video game, much as a capable musician can transcribe a musical score from listening to a performance. But in both cases, there’s no substitute for the original document as a direct line to the creator’s intentions and work process. As such, it has both practical and historical value, to the small subset of the game-playing/music-listening community that cares.