Wow, you have the elements here for a really good photo. Deep blue sky, interesting clouds, silhouetted subject, and lens flare that is not obnoxious but actually adds to the composition.
Compositionally, I really don't think the vertical crop is working well here. I don't know what was on the left or right of the crop, but if it was "empty" I think a horizontal crop would have made shot seem more balanced, overall. It simply feels "tight" on either side. The eyes go from the blimp to the sun back to the blimp, which is good, but it almost feels like there should be another element somewhere. Also, the blimp seems to be heading out of the frame, which doesn't help the sense of balance or movement either. If it were pointed the other way, or had more "space" in front of it, it would actually be fairly effective at adding some dynamics or "movement" to the picture.
Technically, the shot is well done. As mentioned earlier, the flares actually add to the shot, I think, and the blimp makes a nice silhouette against the sky.
You met the challenge, well, I think, but there were just a few details that would not compel the viewer to stay with this image longer. Well done, and best to you in future challenges.
If I need to further clarify or explain anything, please feel free to contact me.