Hello! I'm going with the assumption that you want to make a realistic image, because it works pretty well as a stylized art piece, that someone would put on their wall. You have some really nice things going on in this piece - the hue changes, contrast planes, and the overall color mood are well achieved.
My criticism depends on your goal, but if you're going for a realistic/believable representation, you should fix the scale of things. For example the people are huge, compared to the windows and the buildings themselves are far too simplistic. You also don't have any perspective, so maybe look into that. Also the iguana shouldn't be able to pierce concrete with its fingers (even at this size :D), so maybe just scratch the surface, rather than make it crack the wall.
Look into values as well, doing value studies will help immensely.
The anatomy of the people you mentioned yourself, but going back to the scale, if you keep the windows, you would have very 'suggested' humans, with no clear features, mostly as vague sillhouettes, almost blending in the window reflections/rooms.
Sorry if I misunderstood your goals with this image, but these are my two cents, hope they're useful ^^
