One thing you can improve upon is that your backdrop mountains look very repetitive/c&p in their silouhette right now (first pic: both left, center right one - second pic: both left, big one and the right ones - (same for third)).
The other would be that you need some texture variation for the ground, especially the green parts. Everything is the same tone mix of green and grey. No earth and stretches. A river or waterfall might help as well, since it would create a variation of colors going through (and gives you a nice centerpiece that could lead the eye towards your big split mountain). Maybe a tip of snow on the top of the highest mountain?
Tree scale has been mentioned, so you know that one.
I really like the valley fog effect, would love a breakdown of that 
Otherwise really great work 