Depth is off - the blurring and sharpening are in the wrong areas. Sections are also oversharpened, and the light-source behind his neck is off as well - that area of the piece should be cast in shadow, not light.
Looks like a thorn bush, surprisingly I really like it...I'd cut down the height just a tad though. As alt said, the depth is off, so it makes it look like there is one flat plane of C4D that the render is popping through. Imo the sharpening is fine, but if you were to try blurring the C4D section that appears to the left of the render then it would look truly fantastic, like a picture of the render going through a thorn bush