This is a gift, just to have. Thanks for posting it. I have very fond memories of playing Wolf3d years ago on DOS. It will be fun to read through the source of the classics.
If you're looking for a high-level overview of some of id's source code releases, check out Fabien Sanglard's guides[0]. He's also written a book that goes into greater detail about the Wolf 3D engine.
His Wolf3D book is gorgeous (full-color, lots of great screenshots and illustrations). Well worth the price. Plus a lot of great info about the vagaries of sound, graphics, and memory architectures on the machines of the era.