I know it's probably something that has been mentioned before but it would be worth loading up CoD4 and checking out their levels. One of the things that makes them stand out is the sheer volume of debris that is scattered around, along with a healthy dose of greenery in the forms of weeds, grasses, potted plants, trees etc.
Are you building your own content or are you working with existing INS stuff? I don't recall there beign that much good debris in the original, so perhaps it'll be worth building some generic models and a decent texture to use with displacements.
I'm also seeing a lot of sharp edges where buildings meet, try to either disguise these or make them less obvious with extras added on the actual walls or corners, things like pipes, wires, posters, windows etc.
Try and make every building seems as if it could be entered regardless of wether it can or not. Again the guys at IW did a great job with making their environments feel middle eastern even if they weren't exactly accurate, they present what you imagine the place to look like.
I noticed a few bits of damage on walls, and it just ends - like someone came along and cleaned up all the mess, where did all the bricks go? Where is all the dust?
The best thing you can do when dealing with such a huge amount of stuff to detail is go and look up some reference (google middle eastern village names, "dirty streets" "bombed houses" etc), pick out parts that look good or have something interesting about them, and build that detail into a specific area; rinse and repeat until everythign is up to a consistently good level.