For me the sketch and the line is really good and smooth, you can probably play on the thickness(?) of the line to create more volume, otherwise I find the sketch/line well :)
For the colors, the problem is the use of blend value and hard value in the same time. Exemple, the in line of the hair is really dark and marked and in opposition, the hair color is really blended. Also, I think the skin lacks value, the lips, the nose, the neck etc, in general the color is pretty flat.
For finish, I think you should detail the eyes more. He look a bit soulless and not empathetic, maybe it is just me but I think that. The eyes are the reflection of the soul so if you want your character to be liked his eyes should be more "alive".
(Maybe its just your art style and the part on the eyes is useless)