Very simple, nice shot that just needs a little more to being attention to the rainbow, imho. You've caught the nice drizzly feel very well and I don't see the fg as oversaturated - after all who's to say what the trees etc in your part of the world really look like? - but because it is so brightly lit compared to the rest of the shot, draws away from the focal point. Trying to make the rainbow match the fg would look too fake, so in this case muting the fg and popping the rainbow a little more would have helped. After all, this was an Expert challenge, pretty much anything goes.
Hope this critique has been useful, feel free to PM me!
I like the attempt to divide the image into foreground and background diagonally, however I think this image lacks a solid focal point. If you could have made that rainbow pop a little more intensely, I think it would be a winning shot.