Very cool idea. I often look at where the banks of streams drop away like this and thought it'd make a great scape.
You asked for criticism though, so here's one to do with composition; I think the transition between top and bottom is too linear, especially with the heavy shadows. Some sort of partial 'collapse' of the top area (perhaps in the area between the ferns on the left hand side) allowing the HC to trail down into the lower section would ease the transition between the two areas and provide something of a focal point.
But perhaps your plans for sculpting the trailing HC will solve this issue in a different way.