http://www.methodonline.com/temp/meth_test_gray.jpg
I would honestly make that lower floor section a smoothed mesh or patch. The kind of surface you have for the floor is tarmac, and that bends to a certain degree. The harsh edge you have where it starts to bend sticks out to much.
Dirt decals are obviously not added but would bring this level out a bit more, all over the place, dirt decals on edges and randomly on the floor as well as debris and rubbish.
http://www.methodonline.com/temp/meth_test1.jpg
While its nice you have bricks there, the bricks dont exactly make sense. Texture the broken side with a rougher slightly different texture, and who us on the ciling where the bricks have fallen from, where they used to be, by using dirt decals to make the area stand out.
The floor again, decals everywhere.
The dirt groups, mud, dust, whatever they are... These can easily be fixed. Either use an alpha mapped model to simulate fade (Can look good, but naff up close. VERY easy to do however). Or use vertex blending and model the floor and dirt heaps as one, blending out where needed.
http://www.methodonline.com/temp/meth_test3.jpg
No light from the fire? Why come? A nice dlight here would set the area off if you lower the ambient tone in the surrounding area. Same as always with dirt decals.
http://www.methodonline.com/temp/meth_test4.jpg
What are those panels? I suggest if they are suppoised to be electrical boxes you make a quick model, because ATM they look very Quake 1&2 Era (Where people used to make complex things from brushes, like chairs, PC's, tables and the like, they ended up looking like, well, boxes of stuff). Again with the blending on the floor, either alpha map it, or vertex blend it.