Composition I think you have the composition spot on here (following the rule of thirds) with the rays of light occupying about 2/3rds of the image.
Technique There is quite a bit of noise and more than I'd have thought from a 350D, 200ISO is pretty slow for that sensor (makes me think this might be a crop from the original?) The light does look bright but did you need 1/1000sec and F/11? This might have been a good candidate for a tripod and ND filters but for all I know you might have used them? I'm with Tlemetry and would maybe have made it more of a 'pastel' image in photoshop. Running though NeatImage or similar to remove most of the noise would have helped.
Aesthetics, Challenge effectiveness The image is nice so, why did it score so poorly? Because 'pastel' is not the dominant colour. For me the first thing I see is a big black cloud covering the sun and then my eyes see the rays of light lighting up the sky. Some time in photoshop could really make the colours pastel and some dodging/burning could make the rays more prominent (maybe even a contrasty B&W image). I bet it was an awesome sight to view :)
Very pretty. I love the sun rays shooting across the sky. I don't see the colors as pastel since these are rich tones but still, I like it. Good luck in the challenge.
Im not crazy about the color tones. I would have altered it in photoshop to boost the blues/pinks better. Looks like the ISO might have been a bit high as you have some noise in the dark areas. I might have flipped this image to show the rays coming downward as we would expect them to be even though they may not have been. I like the shape of the cloud. Looks like a hand holding the sun if it had been flipped.