The big difference between Superstructure and a more traditional Combine style building from retail is that the mod's structures have to look good under a variety of lighting conditions. In HL2 we mostly only saw the Citadel with extremely low key, dark lighting in many places, which obscured much of the actual architecture since it was so massive it stretched up into un-illuminated zones on the ceiling. Five was originally designed with a time of day system in mind, and as a result the maps needed to look good with multiple sky settings and different lights active to illuminate the map during the night.
The mod at this time does not still retain a time of day system, but I'm open to adding one along with free-roam maps after the full release of the game or if I get many more people helping me work on the project. However at this time it's looking unlikely if I ever want this to be a playable product that I can put into the public's hands. Keeping it with one critical path in mind for now, but pushing the limits of my zones to try and do things differently and better than vanilla, with more varied level design, a good sense of place, and an interesting tale to tell.
