Adding a helm may, add some variance, other than that, it's coming along nicely

A helm like one of these? If so, which one do you think would fit better?

Edit: Have begun work on a helmet, decided to go with a Spartan one.

Look good?

It will look super stretched on the texture and will look bad. I suggest fixing the mapping of the head. Colors are meh, kinda good for a new guy making textures.

The eyes are too big and the eyes should be smaller and they should be more down.

lower them more

lips need definition

in your inspiration pic the skin on his body was slimy and kind of leathery. In the head you made the skin looks cloudy almost. For the helm piece the shading should be completely different from the skin but it looks similar. And the mapping needs to be re done entirely, the face stretches to near the side of the head

work on making your shading a lot smoother and get away from using your sketch in the design. there should be very little black lines in the head but to me it worked around where the face and helmet meet

Lower the eyes +

Your only drawing what you think you see, draw what you actually see (by constantly looking between the original and yours) capture shading, highlighting, colors (I'd even use a eye dropper on the original I don't think thats c/p), and most importantly lines