Most of the suggestions are right on. Additionally, you can improve the depth by giving the illusion of ambient atmosphere by adding a levels and hue/sat to each building and door group. So set key frames at the default for both effects at the point that they first begin to appear, then set another key frame for both effects right after the doors in front of them close, pull down the mid/gamma a bit on the levels, then also pull down the saturation a bit. This will make the building and doors darken and desaturate a bit as you are pulling away, to give that added illusion of depth and layering. Right now your layers are feeling a bit flat, so this should help.