U need to learn how to blend the guy in with the backround a little more, try making the green backround silver and make it so that the focal point is in the centre whih gives the corners a fading out feel.

for both theres not that much depth. On the first one the render just sits there extremely flat, lower the opacities and add in some gradient maps or photo filters to help blend.

No depth

Render stands out way to much.

C4ds dont really go witth he render.

Lacks in blending

Use some better c4ds

Try to use and actual background. Buildings, fields, whatever fits