I Like the horses a lot. Too much foreground though (grass) - can you see how it would be better if the grass was less and there were more trees and sky above? Thirds again.
The top white flower is interesting (technically). You have the same problem with that that you have with the dog rose in the top sequence - its "burned out". This is because the flower is much lighter than the background. The camera is setting the exposure to the average and the background is too dark and the object over exposed. There are three ways to deal with this
Most good digital cameras let you over-ride the exposure (mine shows -1, -0.5, 0, +0.5 etc. in the view finder. Don't worry what this means, but if shooting a bright subject against a dark background, reduce the exposure (like your flowers). If a dark subject on a bright background (a bird on a branch with a bright sky behind) you can increase it.
You could also use your body to cast a shadow over the flower. This is why the pink and white flower is better (although blurred which indicates a slower exposure due to less like and some "shake". The lower white flower is also better as its in shadow.
The third way is to change the exposure by darkening or lightening in your software.
You are right about the boring one - there is no place in the picture for your eye to settle and nothing in the foreground. Imagine a birs breaking up the blue sky and a hawthorn bush breaking the sky line to give some foreground interest.
I hope this is useful Leon - I'm not trying to criticise - just pass on a few tips.
Red