I think the darkness is intentional. It's just before a storm, and it does a pretty nice job of capturing the golden light sliding in under the storm clouds to illuminate to rock face.
The biggest problem I see with this is that the sky, land, and river are all roughly equal. One should dominate, the others support -- it hardly matters which, they're all fine subjects in this. Crop on the bottom to leave only a sliver of river at the bottom for weight and interest. Crop on the left to eliminate the larger region of sky. The land is excellent, and also quite difficult to crop out, so it's got to be pretty much a sky/land or a water/land photo, with just a touch of the third element (for context, and because you can't crop it out anyways).
I think this would also benefit from a little more contrast in the darker region of the cloud above, and in the band of evergreens.
Also it's a bit soft etc. It's probably worth sorting through those technical problems at some point, but for this particular image if the softness isn't a processing artifact you could simply embrace it and render a soft and moody landscape. The era of "landscapes are required to be sharp" is finally beginning to fade, thank goodness.