Yeah it's a well composed picture. Professional photographers
  know where the "gravity" of a photograph should be and where
  there should be less of it. Considering how long this type of
  composition has been used in photography, there's no way to
  really know if we weren't just trained to see this as balanced.
  Ye ol' nature/nature stuff. In the OP, though, I see a diagonal.
  Bottom right , upper left. Something interesting in lower right
  hand half, something interesting in upper left hand half. But I
  tend to split things down the diagonal anyway.