One thing about aprq2 it has celshading..
And imo it gives other player a nice advantage to see aliens better in gloom
well not as good in dark but bright areas you can perceive them
much better
with celshading enabled. I know that its nice effect for some but.. I consider it as a cheat.
some examplesWhich one you can see better:

ingame:


These I used to test:
gl_celshading "1"
gl_celshading_width "6"