Also wanted to add on since Lightmap was brought up (also suggested
here forgot to link), one map that could really use a touch up is SnowChild especially when you are in the Catacomb, if you have LightMap enabled you cannot see anything and this is much the case if you are playing in Infected mode, to even see in the Catacombs of SnowChild you have to turn off LightMap.
Though, Nagrand_Underground could use a touchup since it is kind of dark in the passageways that you may need to turn off LightMap in normal mode to see where you are going. (I use default video settings)