i think the problem with the tall grass is that its too repetitive, like copied blocks of grass...
just like the tiles on the sidewalk, they are all the same texture, and it shows
also some sky and ground elements, like the guys said: light fixtures, urban elements, some birds in the sky, etc
about the colors, i would tweak it to a little bit warmer colors
it is actually pretty nice as is, but you asked for sugestions to improve, theres my 2 cents