I think the composition is fine, although I am personally drawn more to horizontal landscapes. I like your framing though, and your placement of the horizon. And your exposure looks great...although I'm sure you already know that. The tree in the top left doesn't draw my eye at all. But at the same time nothing else really draws my eye either...seems like there needs to be something else to really put this image over the top, but I know we never have control over what the landscape we are photographing looks like.
All in all, it's a nice shot. Keep it up.