I was going to talk about the beard man, but decided that was a bad idea. :P
Ok, let's see what we've got here...
The thing that primarily and firstly strikes me are the eyes/holes/whateverthoseare. They look very unnatural considering they're just circles filled with black. In real life, we don't have natural circles filled with black. Look in the mirror - even your eyes aren't filled with black. There will always be some sort of reflection from the inside, whether it be from some sort of material or whatever. Easy fix so long as you didn't use anything permanent. Erase the black and put different shades in where appropriate. I don't know what this is supposed to be exactly so I couldn't really tell you where.
The position of the thing is off. Stand back and you'll get what I mean. It looks like the Leaning Tower of Pisa. I mean, sure, it isn't meant to be perfectly positioned in the middle and straight up and down, but surely whatever this structure is it doesn't lean that far to the right. Unfortunately, this isn't something that can be fixed easily without changing the whole thing up.
Yes, the shadows do look sketchy and unnatural. I'm not going to dwell on how to fix them though, because I assume you know how (or at least I hope you know how :P). Looking at some of the unpopular aspects of your shadow use, they aren't very dynamic, but I can see a shadow pattern like this used anywhere in the real world, which is a huge plus. If the shadows weren't so dang sketchy, I'd know how much brightness/darkness contrast is there, but because the shadows are sketchy I can't tell exactly. From the looks of it, I see a healthy amount of contrast though. The only area that might need a tune-up may be the space directly under the chin/nose on the head area. That could probably use some darkening. A softer pencil will do you wonders.
The, uh, hair/volcano thing is... odd. I don't know what it is. It just seems out of place. *Moves on because he can't think of anything else to say*
It looks like you tried to pose a basic, centered format, which isn't necessarily a bad thing but you didn't do it fantastically or anything. The shape isn't symmetrically accurate enough to pull a good centered look. The spikes on either side of the head don't correspond to the other side in terms of size, which is pretty distracting to say the least.
The bottom part is busy, and I don't have anything to say that isn't extremely specific. I guess the thing that stands out the most is the fact that the shadows make the details on the right side blur together in a blob fashion. Same deal on the left side - the lack of shadow (which is probably intentional and good) causes the detail to look washed out.
The background is strange. I... don't have anything to add there. I think you know what's right and what's off. Well, that and my fingers are just dog-tired from typing this post.