A few things I think about this map:
The name needs to be changed, since it's not a valley although that is a minor detail.
Players would not be able to see the invisible blocks in the second section easily, and the white clay underneath looks out of place. Invisible parkour is beginning to be overused in my opinion, and is usually quite unnecessary. The exceptions to this include parkours which are meant to be invisible like the mirror parkour, and invisible parkour; or those which are meant to be extremely challenging or puzzling.
The ground is just flat and lacks detail. While it's nice to see a border around the (edge somewhat), the middle could use more dimension. Make it have areas where it goes up and down and isn't just flat. Also, all the edges are the same. I think it would look better if there were some variation.
The trees are all very similar, but more variation would be nice.
Everything just looks gray and brown. I would like to see more color, or more contrast in colors.
The slime houses seem a bit odd. It would be better if they were a bit larger and weren't all very similar.
Remove the
nether portal in the corner, it doesn't fit the map.