1 - I like how the sandy path leads the eye into the picture. However, IMO there is no real subject in the picture. I like the fluffy white clouds in the blue sky though.
2 - Poor black and white conversion. It lacks contrast. It looks very flat and again there is no real subject to look at.
3 - Does not do much for me (it is a picture of a seagull on the beach1). In terms of exposure you did well with the difficult back lighting, which can sometimes be troublesome. Watch your horizon!! It is horribly crooked.
4 - Again good exposure of a back lit subject. The light is interesting but putting the tree right in the middle of the frame does not work for me. Moreover, I don't think the shape of the tree is strong enough for a successful silhouette