Slashdot links to a technically crunchy code review of the iPhone port of the classic first person shooter. While this is probably of greatest interest to game hackers, I actually am most fascinated by the comparisons between how Doom originally solved limitations in contemporary computing resources and the very different runtime the port has to tackle.
There is plenty of trivia peppered in amongst the bulleted lists, code snippets and detailed diagrams. There are even some explanations of how games that succeeded Doom, like Quake, evolved to handle problems they had in common. Not surprisingly, the original Doom sources are well commented and the new code written for the port seems to carry forward that tradition.