Not sure why, but the colors just are not sharp enough on this image. Perhaps a little more post processing is necessary to really make them stand out such as the lime green on the black baloon or the brightness of the orange?/red of the pumpkin? balloon in the middle.
I think this is a nice shot but really what comes across is a feeling that it was taken a short while too early, and I wonder if waiting for the balloons to be moving away would have created a more dramatic image.