I think what's holding your faces back is that you're not sketching in the sphere of the eye before drawing it in. Remember that the eye is a three dimensional form, and the eye lids wrap around the spherical surface of the eyeball. There's also a lot of inconsistency with placing the features of the face (in terms of placement, angle etc) . You should try doing the musculature of the head (rather than just the skull) to help with that.