-Very realistic, specially in forest-like parts, adds that suspense that anything can pop out of nowhere.
-Makes you have that "oh crap" moments when SI spawn far away from you since you can't see them at all (specially with tank).
-Easy to freak out when horde surrounds you in certain places since its pitch black (on higher dificulties).
-Works amazingly with glow in the dark skins/models.

-Some skins/models won't be as apriciated as usual due to the complete darkness as opposed to glow in the dark skins/models (no points deducted though).
-Default flashlight isn't bright enough, had to use a birthter one.

Overall amazing mod, it really puts your sense as to what might be lurking around and gives that tension and suspension-like feel that the game desperately needed.