I'd say more variation. Cheat a little for the benefit of overall look.
For example, on the background with the watertank (?) against the wall, throw a crack in here and there and maybe some brick/plating lines here and there to give it more texture. that kinda thing. If you're feeling like giving it a more opressive atmosphere, some smoke in the distance now and then could give it a more storied look.
Minor alterations in the tileset like that can do a lot for keeping it all visually interesting.