this is a very strong piece and you stated that you were experimenting so i'm going to skip the cordial points and get straight to the nitty gritty.

Cities aren't quite the concrete jungles that artists make them out to be. very subtle hints of varying colors in the cityscape could have made this piece even stronger. I would have liked to have seen the effects of exposure to prolonged sunlight and dry rotting on the colors of the city as it aged.

I agree with the previous critiques in that more erosion and wear would be expected as well as more variety of color in the foliage.

dust/particles in the air and a thicker haze in the first panel that transitioned to sharper cleaner air would have been a good touch.

i recommend using more human artifacts other than signs and automobile's which don't carry as much of an emotional weight to the viewer.

all in all, a very stunning piece for an attempt.

Well, as it seems your goal here was to show a passage of time, I have one simple critique. It seems that the only indicator of the passage of time is the moss and other plant growth, and while yes, as mentioned in the comments, mother nature does repair herself, I think a few more indicators of the passage of time would make this even more successful as a piece. For example, on the sign on the right hand side of the image, perhaps show it increasingly more crooked, or the ramp or broken piece of street near the center show it having crumbled a little more. Perhaps use a few softer shadows on the defined corners to show some erosion from weather as well. Sometimes it's the small things that make a work even better.