The grass texture and trees shadows' shapes makes the terrain on the background look flat, losing the perspective effect. If you notice the reference, the further the trees are from us, the more their shadows change from blobs into horizontal lines. The grass on the furthermost terrain is rendered to show the same detail as the one closest to us, which also removes depth effect; try suggesting texture through smaller and subtle grass shapes.
While the whole piece looks great, there seems to be a discrepancy of styles: the trees look cartoony, with large blobs of color, while the grass looks realistic. Just stating that
You could push for more depth on the leaves by showing greater contrast between the trees' groups of branches (not changing the colors, but having big changes in contrast between leaves of trees at different distances from the observer).
Great rendering, palette and texturing!
