If you have installed the QEffectsGL files and graphics don't look any diffferent try this:- 

•NVIDIA drivers sometimes use profiles for the games; they pre-load system's OpenGL library before the game 
loads it, and the wrapper is ignored. To deal with this, try to rename the executable: e.g. rename quake2.exe
to quake2_.exe, and use it to run the game. Please also rename the corresponding entry in the
QeffectsGL.ini file for the game!

This info comes from here :-

https://github.com/crystice-softworks/QeffectsGL