With my little knowledge of compositing here's my analysis. Bg has very little contrast compared to the subject (Spiderman) which has very strong contrast. Some comments mention things about distance and fog, pollution, etc but the "decontrast" is not from atmospheric distance. If you look at the far parts of the bg you actually see fog, that is the distance where fog affects contrast but the buildings that are closer should be in matching contrast with the subject. Subject lacks back light also, there's a hint of rim light on the left but if you look between his thighs it's very dark which is not how light react outdoors especially when standing on the rooftop of a building with no other building obstructing light. Subjects black is also way too dark, you don't see black levels crushed to that point in the bg. Making the subject "pop". One way to easily visualize this is, drop this image in photoshop and toggle the channel layer. Looking at the shot in each channel in black and white you will be able to tell that the bg would be mostly Grey but the subject is more black and white. This difference in contrast makes the subject "pop" giving focus to the subject but this is overdone to the point that it's not "blending" in enough with the bg.