#1 As others mention that green is overpowering. You need to identity what you want to showcase. Either the trademark green scottish grass or the abandoned building. For me the building seems to be the main subject so I would tone down green and reduce brightness on the green and add light on the building. Did you use GnD filter in this shot? There seems to be a dark band going across the frame. The dark banding wouldn't matter unless it is on your main subject and /or is distracting.
When the main subject isn't properly aligned with horizon, HDR may be a better option to go instead of GnD.
#2: Apart from the blue color sky is rather bland and there is too much vignetting around the corners. Foreground is interesting. I would have kept more foreground in frame and less sky. Secondly the crop at the bottom is distracting. You should have frame complete footstep.
#3: I again see dark band as if GnD was used. You need a polarizer to control the reflections off water. You can also try to work with the scene to use rocks for creating interesting compositions. For e.g. one rock leading eyes to second rock, then second rock leading eyes to water / scenery. It is just an example, you can try to play with the scene.
#4: This is my favorite shot from the lot. The colors are beautiful in the sky. The foreground however doesn't look very interesting. The cracks are taking eyes out of the frame. You could have reduced foreground a little. It would create more powerful image.
Hope it helps. Not to mention, its just my opinion.