nice pic. just a tad soft on the focus. i really like the mountains as the backdrop to add to it's airyness. i wish the bush wasn't there, perhaps it was impossible to get an angle without it.
i've never tried shooting something like this, but a couple things that might increase the drama would be lowering your camera angle so the rider was above the line of the trees, and opening the photo up to the right a little more to give him more space and so he's less centered. I like the rider's pose, the DOF, lighting.
Nice action capture and good composition. Lighting seems a bit flat, but there's nothing you could do about that, I guess. I bet whoever the subject is would love a copy of this shot!