Take notice to how the hair in this picture frays to one side of links head as well as the different mid-tones to the strands in his hair in the picture below.
In your preview you kind of clump the hair on the forehead of your character as opposed to letting it flow naturally, it kind of looks like a liquid is leaking down his head.
As you can see instead of actual strands, in the lower-poly art (above) there are simply darker lines to achieve the desired effect, try adding more contrast and experimenting with honey color (or auburn) [#F4940C or near that] to get the kind of look in the picture.
