Enviroment (bushes + trees, screens 4 & 6) from third person perspective is sexy. Reminds something Valvish, like wastelands in HL2 or something from L4D. Unfortunatelly, buildings are not. Too clean. Too many empty space. Make a hole in the walls, piles of rubbish around it! Pipes, broken and leaking! Bridges over holes in ground make from wooden boards and similarwaste materials. Holes in concrete with plants growing through them (broken concrete, orange grassy dirt tile and grass prop from river rushes) And variate testures.... Maybe some sources of darkness \ lightning, have a look at "not so modern" raid1000's zombie screen in his gallery.
P.S. Have a look at screen 4, you grass props have shadow. WTF?
P.P.S Fro rubbish use barrels, including wooden, crates, empty and not, broken campfires, some stone decorations, scaled and recoloured to look like pieces of surrouning "modern" enviroment. Hell, take some crystals from Icecrown, scale them to look flat -- broken glass! You'd need more than one copy though, stack them on each other. From Ruins of Dalaran, houses "sceletons" -- lots of wooden planks stacking vertically, looks great I must say.... Some other "broken" props, like broken wheelcar, broken fountain... In that barn you can spread hay across the floor and put some "farm-like" props, like mentioned broken wheel-car, sceleton horse, I dunno, maybe import something.