step back and check your angles. details and negative space. looks like you have stared at it so long you are lost in posative sapce. It is great but the angles around the shoulders and the angle of thhe helmet. the slightest mistakes between the distance from the nose to the mouth (yours is fine, it is just an example) can be a huge differance and look to an objective viwer. There's something wrong here, its your model and not yet made enough to make a real comment except, great, but somethings wrong. work my friend work and all will be revealed.