That's NICE! The palette works well. You let yourself be inspired by helm, no? I mean the use of those 45° lines seems pretty obvious, but also the palette does remind me of his stuff. I love the skull-like facial features; the background on the other hand isn't my cup of tea. I find this blocky stuff, especially that pile to the right almost obstrusive. I'd go for something fainter, maybe a little less random and more simplified even. That brake at the bottom could be used as thorough AA-practice, if you feel up to it :).
I'm not sure if I agree with equinoxx on the harsh shadows. I mean it should work if pulled off consistently, and I can't spot any major irregularities, but if you look at it some time it does stick out. The fading dark arm itself looks good though.