Hey all, as I answered this post: http://www.gog.com/forum/sin_gold/too_dark_any_gamma_controls
I had a thought as to something that could explain the black screen problem. I've sent the details to GOG support anyway, so hopefully they'll update the game to use nglide 1.02.
But anyway, yes, the included version of nglide, 0.99, uses a configurator which writes the settings to the registry. The OP of the thread I've linked to says that the gamma settings in 0.99 go from 0.8 to 1.2, so that's 5 options in jumps of 0.1. The setting in the registry stores the values 0 to 4 for these, so the default for gamma 1.0 is value 2.
Now version 1.02 (the latest) on the other hand, has 11 options for gamma, from 0.5 to 1.5 (in jumps of 0.1). The default for gamma 1.0 is therefore the value 5. This value is out of the range of the earlier version.
Now as GOG have released some games with nglide 1.02, and as both 0.99 and 1.02 write to the same registry entries, this could be the root cause of the problem. A later nglide version writing a value of 5 for default gamma, then this game not being able to understand that value as it is out of range. Also why updating it to use the latest nglide fixes it.
I've attached a screenshot showing the two configurators for nglide. 1.02 has saved the value of gamma = 1.0 (value 5) in the registry, and version 0.99 then shows a blank as it doesn't understand what value 5 corresponds to.
So, mixing up nglide versions in different GOG games has probably caused this issue.