Nicola, welcome!
Your first is a nice image and I like the layered effect of the mountains but I think it would be much improved if you could open up the shadows, particularly in the trees on the left. It should be pretty easy in PS or Lightroom.
I like the second very much, but again it's a bit on the dark side.
I don't know how you have managed to get the clouds in the third to appear as they do, with the black blotches around them, and I don't want to know: they really don't look at all good.
Jeremy