It wasn't ever photo-realistic. Why bother with realism at all? This looks awesome btw http://www.quelsolaar.com/love/screen_shots.html? There was also a gory black and white and RED game that I can't find right now.
While no-one would argue that Quake was truly photorealistic, it was as realistic as the hardware of the day would allow at a videogame framerate (30+fps).