it is a cool wallpaper.

some things come to my mind which could be improved. looks like you made the dof effect in a post by blurring the front and the back. maya can do better. you should focus on the helmet, and increase the fstop to higher than 11, if not even 22. this will create a noteable, but decent depth effect. if it comes to placing the helmet, dont put it exactly in the middle. it will look more professional if the center of interest is NOT in the center of the image.

keep it up