Underground tram station

I've been working on a scene for quite some time now, and have pretty much hit a brick wall, as I can't seem to be able to add more detail to the scene without making it look terrible.

I've posted three pictures of its current progress in one of my galleries.

If you can give me some tips for improvement, I'd really appreciate it.
(I do know that most of the textures aren't right, but I can't figure out what makes it wrong to know how to fix it)