Marie, in general terms, what I think is missing here is light. IMHO, unlike most situations, these sort of shots generally benefit from very contrasty lighting. For instance 2, 3 and 5 would begin to pop if there were strong shadows - particularly the fire escape if the shadows repeated its shape on the wall. The first shot might benefit from a crop and some perspective correction as has already been suggested. It's also a bit flat and so the contrast could be boosted - see below - but even so, it's the small details that can be a problem. For instance, for me, the fact that there is still a fairly prominent sign pointing out of the composition bothers me a bit. Hope that this helps.