Don't take this as an insult, but you haven't mastered drawing by any means. While the representation is better in your sketch, there are still some fundamental issues evident with showing volume and form well. You are still drawing things according to the way you think they are rather than from an understanding based on unbiased observation.Things like the lips and eyes, skull structure and even hair are a simplistic representation of the particular forms lacking a sense of true volume and form.
You are doing a fairly typical thing of trying to take on more than you have done the practice for and feeling disappointed for it. Don't be. I haven't seen your progress but I would say to begin with definitely do more study on constructing the basic forms and shapes that make up the various features of facial anatomy and head construction. This and only this will help your skills for portraits all round. This and do lots of studies of portrait paintings by masters and from life and /or photographs. I recommend Nathan Fowkes' s charcoal portraits for great understanding of how just simple value and shape mastery can showcase form in an exquisite way. Sargent is good for portrait studies as well but find what you want to study foremost in the field and go for it that way.. There is no shortcut to practice.
In terms of digital painting, your tones for skin are too homogeneous and skewed towards the red. Start with this link and make sure you go through the other 3 sections as well.
http://navate.deviantart.com/art/SKIN-a-...-144294636
Your enviro is showing a lack of understanding of perspective so I would start there with your study. Loomis is always a good general all round resource. Your colours are too saturated imo and values could do with work. Get james gurneys book on colour and light for a good intro to lighting and colour, lots of good stuff on his blog too.
Keep drawing, keep studying, keep painting if you want to improve.