Definitely, critisicm for this cover is easy and obvious.
The green is just laid on a little too heavy and much. The concept and layout of the cover is good. It's just there is little to no contrast of colors on the entire cover (minus the items in the bg). The whole thing is green basically, which doesn't look too good to me. Maybe make the text an alterning color, work with some different ones.
Secondly, a small little nitpick, but his entire face and clothing has a greenish tone, yet his left hand looks red, as if you just forgot to alter the coloring of it.
But overall, nice job, just a little too muc green as others have said. If you saved the PSD w/ layers, as you probably did, you could just go in and change the hue of some of the overlaying items.