here's my feedback: (by the way how do you make those pictures from scratch, i'd love to know
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1) I think it's quite good, but a bit too much contrast with the colours, maybe dull them a bit, and maybe the rocks stand out a bit too much, look a bit "too" 3d.
2) I like this one, it would go well as the floor for a level, but the moss looking higher than the stones, it doesn't look natural imo, maybe (somehow) make it appear lower than the rocks, then it would look v nice
3) I don't particularly like this one, it looks very 2d and dull for wood, real wood is more . . . lustrous, more deep in hue. also those are very long and thin planks 
4) This one is the best, its only problem being it's not 3d "enough"
. . . The smaller and larger rocks look awesome, but the effect is undermined by the seeming lack of depth. the colours are great though.
hope I've been useful 