Looks pretty good, although I don't like some things on it. Such as, the shading. I really don't like it, also with the lines, they look very incomplete and messy. Other things I don't like are, the simplicity of it and the eyes. Unless simplicity is what you are aiming for of course. But I still really don't like the detail of the eyes, they should have more depth and shading also. The gas mask, really doesn't look like a gas mask at all, to be honest mate this is pretty poorly done. Although I do like this, I think you can do better. There are other thing I can spot out, but I wont.
Still, nice work mate. I'm assuming you are a beginner, if so, you seem to be on your way to a great head maker. Keep it up, as you can only get better by practising. I hope you take this criticism the right way, as I am not bagging you out. 4/10