You guys really are professionals. This map is like a living painting.
I love how the tunnels and outdoor areas are organically fluid from afar, yet still retain believable roughness and detail up close. I notice the little patches of moss and grass in screenshot #05... Those small touches of green really help to turn an otherwise drab scene into a sort of hidden underground oasis.
I really like how you guys made the sharp surfaces of the ruins' structure flow and transition so smoothly with the caverns and ruins. You made the ancient, worn-out aesthetic work well without making it look trashy or ugly. Instead of rotting away into nothing, these ruins have ripened with age like a fine wine. A+++
The level of detail that you have put into every interior surface really shows a great level of care and thought. There isn't a single wall or floor surface that looks plain or boring. Everything looks like you could almost reach out and touch it. The subtle meshing of the corners of the wooden pillars and rocky blocks give them tangible edges, and the bump mapping everywhere gives the scene depth and texture.
There are only two areas I can really critique... In screenshot #07, the brick pillar nearest the center of the frame has some mirrored textures that break immersion to a degree. The same meshes with the mirrored texture also make up the pillars in screenshot #04. After correcting the texture on that particular mesh, I would suggest rotating and/or flipping the pillars in #04 individually so that they don't look quite so copy-and-pasted. Adding one light source near the upper half of the center pillar there might also help to break up the regularity a little as well as make the scene 'pop' a bit more.
I can tell that you guys are passionate about this project. A lot of love was put into this map, and it shows.
P.S. You should totally think about building a spaceship map eventually... A whole bunch of the assets from Boxfield are already perfect for the task.