I was about to post this.. (see in yellow)
But it seems you beat me to it
In addition to what Hirazi said, there seems to need a bit of "cheekbones" or some heightened curve under and following the eyes from the eybrow to the nose
You know, you can also have a grid with your reference as a texture, and select and hide the back of the head, and then adjust proportions and features in front view while having your model in wireframe mode (grid in textured)
Or of course while having your ref as a rotoscope viewport background.
In eather case, you can also sometimes go in shaded mode, and hide/unhide back and forth repeatedly to more easily see the differences in shape etc..
Last point, it often seems like your model is lowres, not because theres missing model rez,
but just in case you didn't know, you can increment 1 subdiv step by tapping "+" (only on the num-keypad) without otherwise affecting your mesh.
Otherwise, pretty good job!
J