I'm more confused but why seems to be ignoring (or just being modest?) the technical feats of Quake and Quake 2 and (what I read to be) some sort of "well we just somehow made it work, but the game development (maybe artistic) was the thing" - and I mean, he wrote them - but for Q1 and Q2 working so flawlessly, not crashing, good netcode... for the huge amount of multiplayer I think the revolutionary tech was more important than the art style, even if it pains me to say it. We also played it long after better looking games had come out.

I doubt you'd get the easy moddability into an engine with AI, one of the huge points for the longevity.