I've looked over this code before. It's... eh... decent, I guess. There are plenty of tricks and hacks that make the code fast enough to pull off a really awesome video game -- and I don't dispute whatsoever that Quake II was an awesome game -- but it's hardly a shining example of clean, well-architected code.
It got the job done and made Carmack and his coworkers a lot of money. That's all well and good for Carmack, but you're not Carmack. You should set your sights a little higher if you're looking for examples of well-designed code.
