Don't get me wrong, I like dark maps too. They create atmosphere.
The thing is, if its so damn dark that you can't see if there is an obstacle right in front of you or where the end of the map is, then gameplay is affected because you can't navigate and tactate (is that a word?) as good as in a day map anymore, and that just takes the fun out. Also, if walls and the ground are just black, maps are a bit boring because you can't see the texturework - thats actually the reason why the "very" bright screenshot is fine for me - its the first in which you can see the ground structure. If you want less color, fine, then lower the light sources in the buildings and not the ambient.
Technically my argument is the following: If ambient is dark but not rgb (0 0 0) then you can adjust it to your monitor by the gamma scale. If its (0 0 0) then at gamma 100% it's still 0 0 0. Isn't that correct?