I think it’s a bit too dark also, but overall I like it. If you need suggestions, i would suggest to play more with a sky and you could also put something in the mountains to make it more interesting, small house, castle or just a small bright reflection of hidden treasures
The idea of putting houses did cross my mind. I might consider re-working it in the future. I think I will work on the lighting though to make it a bit more bright, but I will do that in GIMP