Thats a very beautiful capture, depth and clarity are good too. But if you think of bettering this shot then I would suggest that the clutter in the fore ground and right side is cropped a little. That will make the rainbow and waterfall itself standout....
jawdropping. I actually got both of yours in the VB, the other one first; but I really like this one more: I think it gives more width to the viewer, and in case of Niagara it's more important than the vertical. awesomeness.