For me, reading the source code was part of what made the game fun. It was a sort of metagame, learning how to cast "real-world" spells by studying the arcane tomes that held the secrets of the universe. It by no means made me invincible (my death/ascension ratio was still topheavy) or even cut out the mystery; it just moved some of the action and exploration from the game screen to a text editor. Two games in one.

Every 5-10 years I end up losing a couple days to NetHack. I'm overdue.