Hey Sasha,
I think this one is awesome! I mean, totally awesome!
Not a thing I would change about it. I love that the rainbow is so huge and translucent. The background being a bit soft is perfect because it then doesn't distract from the focus of this shot, and that is the rainbow. It provides a cool backdrop to the rainbow with the cliffs, but it doesn't distract in any way.
You should really think about entering this in one of the annual landscape contests, like with Outdoor Photography, or such.
Jim