Nothing about Quake, but 3D gaming in general. I love level design, and since there's practically no 2D games out there, I have to move onto 3D. The BUILD engine (Duke Nukem 3D, Shadow Warrior, etc.) is arguably the easiest-to-learn 3D engine, and there's still a Duke 3D level design scene. Designing levels for Quake looks plain fun.

Anyway, I take it that the majority of the community wants me to make a single player level (it'll probably be two or three extra large ones, think EvilMike's level pack series). I'll get to work.