What I imagined with regards to tunnels and spawnrooms and generators...

[Figment]

Something like this perhaps?



Notes:

• SCUs in my mind are strategic objectives next to the spawnroom which control the local spawn shields. They should be possible to disable with sufficient explosives (IMO only infils should be able to hack them as this would be the stealthier way of taking them out).
  
  The SCU of the Forward Barracks is purposefully easier to take out than the main spawn room's SCU.
• Killing a SCU would drop the shields, but not the painfield.
• Generators too should require explosives to kill (again, only infils should be able to hack them).
• To take the vpad shield out, you either need a vehicle with shield breaking capacity, or go through another path (like the top floor or back area).
• The shields are primarily there to keep AMSes out of the courtyard in the first stage of the attack, until a shield gen is busted.
• I still would like to see a Sphere of Influence over a base, so the Galaxy would get a much greater role once more in strikes.
• Pondering adding a Main Generator somewhere in the tunnel system, which would control spawns, turrets, vehicle and equipment terminals, but would take a 5 man squad worth of firepower to take out.
• Corridors would be five men wide and littered with objects and possibly manholes (opposed to two men wide in PS1 and just manholes on the side).
• There are many ways to get in, many ways to get out. Camping all exits of the entire complex would take a huge amount of troops. Holding all exits would also require quite a few players, but most of the interiors can be held with less troops at choke points.
• Due to the depth of the tunnel systems, medics become more important, so would ammo packs and engineer's turrets (ideally, they would still get some sort of numerical limitation!).

Disclaimer:
Done in a couple hours and only shows general connectivity, not extremely specific corridors or stairs as putting that kind of complex 3D into basic 2D is pretty hard to do. Hence it also misses blast walls, etc. It's basic, but should give you a pretty decent idea.