Hey Stuart,
Replying from Bryce....looks like you had excellent color and while the bottom of the flow being truncated does bother me a bit....the image appears a bit soft overall which is surprising at f11.....so try runnung some more USM on it. I do wonder if you turned the polariser too to maximize the effect on the water......as the FG water has a bit of glare on it. I feel this image is almost devided in 2.....both halves being very good but combined not working for me. Don't get me wrong.....it's not bad.....I just think it would be stronger with either a higher perspective to catch the base of the falls or concentrating on either section would be stronger. Colors look great so I hope you explored multiple comps.
I love the contrast of the fall colors with the green moss. It could be oversaturated, but then I get tons of saturation with a polarizer on an overcast day. The composition problem that others have mentioned here holds true for me as well. The biggest problem is that my eye doesn't flow easily through the scene. The two foreground rocks and the water reflection is welcoming, but then I get blocked by the middle-ground boulder. My eye can't easily move around it and up the waterfall, taking away from what is an otherwise lovely photo.
As Roman suggests, perhaps moving to a higher elevation would have helped, or perhaps left or right to get around that large rock. Then again, perhaps it just doesn't work from this side of the falls - mother nature doesn't always deal us a full deck of cards! :-)