|Greetings from the Critique Club
What an interesting idea for the Square Crop Challenge; Circles within a Square.
While the idea was a really good one, I'm afraid you had a little problem with execution. First, as your commentors mentioned, your image should be square. That is, all the pixels on all sides should be "640" or some other equal number. Because voters didn't think you met the Challenge, this doomed your image at the start. Then, it's important to have at least some of your image very, very sharp. This gives the viewer's eye a place to rest. If he doesn't have this place, he just keeps going on to the next image, never taking the time to enjoy the idea you have presented.
Finally, when you request a comment from the Critique Club, it is important to include your camera settings, and also write something about your thoughts in the Photographer's COmments section. This helps us understand what you were going for, and in addition, helps you to understand your camera.
I wish you good luck in your future DPC entries.