I do have my in-game brightness turned all the way up, 'cause I can't see much otherwise, so maybe that's the reason. It's normal Nether lighting, the server cannot do much about it - it only tells the client whether the world is Nether or Overworld, and the client does all the lighting.
The code is in the SVN, activate it by setting CompositionGen to Nether. Note that the generator still observes HeightGen settings, so you can actually have a Nether with irregular "roof". But then it's possible there'll be opportunity to dig out, as the roof is not contiguous.
Also, in world.ini set world dimension to -1 for Nether, 0 for Overworld and 1 for End (affects client lighting only).
The code is in the SVN, activate it by setting CompositionGen to Nether. Note that the generator still observes HeightGen settings, so you can actually have a Nether with irregular "roof". But then it's possible there'll be opportunity to dig out, as the roof is not contiguous.
Also, in world.ini set world dimension to -1 for Nether, 0 for Overworld and 1 for End (affects client lighting only).