It does feel slightly oversharpened, but it's not about halos it's just an overall sense of busyness in the details combined with relatively flat global contrast. This could just be a cloudy day combined with a busy subject, though.
This is certainly an interesting structure, and I see what appealed to you about it. The juxtaposition of the flag with the building is interesting and raises questions, which is good.
What I am not getting from this is any sense of eye leading, there seems to be no visual center. The arrangement of forms is not particularly fortuitous, this looks like you simply set up wherever was convenient to cram the bits you wanted into the frame (and I concede that we are often constrained in where we can shoot from). Our eyes are not led to the important symbol, the flag. One way to say it is that there is a strong intellectual center at the flag, but it is not a visual center, and seems if anything to be an anti-center, visually. Our eyes are virtually driven away from the flag, it feels concealed in the welter of detail. You're forced to use a gimmick, selective color, to bring us to the intellectual center since the arrangement of forms drives us away from it (this is one of the reasons selective color is problematic, it's often an effort to save a failed image).
There's a solid idea here, and I dig what you're trying to accomplish. Having an idea at all places this image head and shoulders above most of what we see on the internet, make no mistake.
I just don't think you hit it with this exposure, there's just not enough stuff pulling together in the same direction to make it gel around the idea.