I really enjoy this piece. It's a great example of minimalism that often isn't seen in deviations nowadays. A great capture of motion, and your decision to use Black and White really helped here with the contrast of light and dark.

My biggest issues would be the concept as a whole and just a few minor technical details. While it is done well by comparison to other pieces, I do find the idea of a "lone window against a stark wall" to be a little overdone at this point. One the whole, it works here because of the fluttering and tone choice, but there have been more original choices.

It also seems ever so slightly tilted. I can't tell if it's the way the window was built or not, but the top edge is definitely not parallel to the top of your frame. The bottom line isn't as harsh, so it's a little less noticeable. It by no means ruins the picture or anything, but it's there nonetheless. I'm also a little conflicted about the wall as a whole. The window itself has this great contrast with definite shadows and depth. However, it tends to make the wall completely flat by comparison. It's probably much richer in tone on a large print, but for internet viewing it's almost distracting.

Again, on the whole a wonderful piece that really stood out among the others when browsing that really only has some minor details that could be tweaked. Great job!