COMPOSITION
I really like how you have framed this with the trees in the foreground. Not only do they providea natural frame, they also help to establish depth/distance in the picture, and add interest. I assume you have a valid reason for having this vertical, but I find myself wanting to see more on the left and right, in a horizontal fashion.
TECHNIQUE
The focus and color on this are nice. This would be an awesome shot with a nice blue sky, but I understand that you can't control the weather. I would, however, remember this scene and try to re-photograph it if you could, with a nice sky, or even a sunset/rise. The trees on the far side of the valley are a little dull. I live in the Southern Appalachian Mountains, and this is a problem we also have frequently. I have found that a polarizer can sometimes help, as can a neutral density filter because they allow me a longer exposure time in brighter conditions. Someone below mentioned a haze filter, which would probably also be extremely helpful, though I've never used one myself.
Overall effect
A great shot of a location that I would very much like to visit!