It's a bit too plain...put some more C4Ds on screen or lighten or something...I don't know...sharpen the focal only...
looks nice but one very small thing that i think should be changed. Take a regular soft brush and smudge the edges of the smudge. It looks very cloudy. Other than that, it looks great.
The C4D you used in the top left corner looks very out of place. Add in a straighter C4D and it will have much better flow.