A couple of things springs to mind. You could have a go with some watered down dark brown between the sandbags, to make them more distinct.
You should also try to get some better pics, you have a nice sharp focused statue in the background but the bunker is quite blurry. Experiment a bit with the Macromode (the flower-symbol on your digicam) it's great for close-ups.
I also think you should have another base, this one seems hollow or something.
Other that this it's a good piece you've made and it seems playable as well. That's something I often forget when making scenery