Hi Daniel, that's some nice scenery you found. Hopefully I can help a little.
1) I like the way the lines created by the wall and valey zigzag across the image and the soft mistiness in the valley bottom is nice and natural. The sky, and possibly the whole image depending on how it was processed, looks a bit over-exposed with blown out highlight areas that have lost detail and a lack of density in shadows. In the days of film, to balance and image like this we would put a graduated filter in front of the lens to darken the sky relative to the land. Now instead we can use a graduated filter in Lightroom or similar editing program, and reduce just the highlights a little, rather than all tones. I might also consider trying another graduated filter over the bottom of the image, but using contrast instead to deepen shadows a bit.
2) The sky is much better in this - the sun will usually be blown when looking at it directly unless there's a lot of murk in the air - but the rest of the sky has retained its colour and the clouds look more solid. Composition-wise I'd have tried to get down a bit lower so the tree stuck up and separated from the background a bit more, and I might also have moved a little further left to sepapate the sun & tree a bit more, and then tried to include the end of the cloud on te LHS so that there was a line of cloud that ran from top right through the sun to point to the tree. As the image is, I'd probably crop some off the top until it 'looked right'.
3) Pleasant pastoral scene but because of composition it lacks a subject for the eye to rest upon. If you'd allowed more space at the bottom then the pile of rocks would be the subject, or if you crop the bottom ones out then the sheep become the subject, and if you crop the tree and rock on the LH edge then the image becomes stronger still. I'd probably process the image to warm the scene a little more to match the evening light of the other 2.
In general guidance when composing images, I think someone mentioned the 'rule of thirds' which sn't a rule, but can be helpful. Think of how the eye enters an image when you see it for the first time, think of things that can help lead it through the picture and the things that provide a focal point. sometimes people will deliberately create an image with 2 (or much) subjects to create a tension, but this doesn't always work so well in pastoral landscapes.
Hope that's useful.