This is my first critique so please bear with me, I will give you as much as I can
I am one to assume that you wish the critique to revolve around the subject matter specifically hair wise?
The first thing that I notice is that the subject matter is highly contrasted, consisting of more lighter tones as opposed to black and white monochromatic. I suppose this comes down to technique or style but in my opinion whether it be accidental or purposeful, it overall detracts from the lifelike realism of an artwork; that is if photo-realism is your goal.
I'll continue the critique with the ideal that photo-realism is what you seek.
In comparison to other artists, I would think your style to be more prudent yet visually rough, as many others seek out similar care however with softness compared to airbrush quality.
Lets keep this short.
The hair is good, but lacks something. As I recall from my own history, I believe that it was said that to create realistic hair you must not only show immense detail, but also within it, an area of contrast in the sense that is dull. I hope this is understood, it requires an area that lacks detail, for the latter to 'ring true'. Now this doesn't necessarily have to be within the hair, it could be a shadow or a piece of clothing etc. Now before you pull me up for being a hypocrite. In this circumstance, the shirt doesn't have this value well because it's plain white. Perhaps if it had some sort of tone then the hair would indeed be more vibrant and alive. But because of the higher contrast it doesn't.
Now I'm no expert and I'm not attempting to be, but if you want to improve the realism of the hair.
>Add greater depth of values in tone.
>Create a contrast of detail.
>Make the hair to be less granulated, which I should say I actually don't mind, it's a nice effect, but if your goal lies with realism then I urge you to soften the hair with a blending stump or something similar.
I hope I have helped you, best of luck for the future