more shadow on the left side of the face (Your left, not the man in the images left.) and underneath the brim of the top hat. Use the burn too to do so. Use the dodge tool to create some highlight on the right side of the mans face and the right side of the top hat. This image is great, but you asked for feedback and I think this could improve an already cool image.

When / if you take my advice and apply it, make sure you make a duplicate file before starting. That way you don't ruin your image if the advice I gave doesn't work. Good luck author.

I think that makes the eyes and glowing part on the hat pop more. Good work, good luck author.

I like the work done for your main figure, but could not figure out what part of the image was the "Boom", It feels like the mushroom cloud is too much of a regular cloud and not so much as cloud of destruction as it is intended to be... if it were my image i would leave the mood set with the blue, but add in some red/orance coloring around the cloud and on it's horizon... this would bring your eyes to the back a little more and give more shape to the doom being formed... great image over all!