It's impressive how the software renderer of Quake II manages to achieve the results as they have them with just a 256 color palette and zero repainting of pixels (i.e. every pixel is correctly painted from the beginning).
The Quake source was a huge source of learning for me when I was getting started. Hacking OpenGL, making a red/blue stereoscopic mod, and discovering pools of particles quickly brought to life and rendered via a linked-list pool.. great fun and so valuable to stumble upon.
Yes Quake II which I expect to be similar is a major influence on anything I do.