Yeah, Meloncov has a good point.
They are really good, solid character portraits and your rendering shows a great deal of confidence but you need to concentrate on your anatomy. Being able to judge an image objectively - especially when you've been working on it for hours - is quite difficult. One trick I use is to hold the image up in front of a mirror. This allows you to see the image afresh and quite often subtle mistakes can become glaringly obvious. When I'm painting in Photoshop I usually 'Flip Horizontal' for the same effect.