The skull is nicely done. The collage effect works because it slightly resembles a real human skull - with different pieces of bones joined together. I like how some pieces are more text heavy than others, giving it some dimensions. I think the outline of the skull is nicely done as well.
I love the inside of the mouth and how it's not completely black. The textures make it seems as if there are screams coming out. The shape of the mouth doesn't match up with the jaws but I think this is intentional. To me the teeth are a little awkward. The teeth are oddly shaped since the molars are relatively smaller than the other teeth - I think this might be intentional.
I have to say I'm not a fan of the background in terms of color. I find that it's a little too similar in terms of color with the skull. But that's just me. I'm sure others like it. However, the style resembles bullet holes and I absolutely love it for that.
The headphone is awesome. The shade of the red works nicely with the other colors in the picture in my opinion. The black part on the headphone appear almost 3 dimensional!
Honestly I really like this collage! This is such a unique and fresh take on collages. The overall theme is pretty clear in your work. I browsed through deviantart for collages to favourite - and to think I'd find it via your forum! I wish the watermark wasn't there though..