This is a lovely portrait -- very expressive. You did a wonderful job. I think what makes Stan's demo portrait successful is his use of lost edges and implied forms. Compared to his portrait, you tend to outline the features with a darker line to show the shape of the form that you have designed. I don't see that as a negative or positive thing, just an observation. Overall, you have a great value range and your drawing ability is really shining here. Great job and hope to see more :)