That looks awesome!
Differences I noticed:
-Missing some knots on the outer ribcage area
-Cheekbones are more flared out than those on the original
-The "cuts" into the sides of the two main head ridges go in further on the original, making it seem like there is more definition between the protruding forehead segment and the twin ridges on top of the head
-The point where the brow segments meet at the bottom between the eyes is more pinched together on the original
-The cheek flaps have more of an axe-blade appearance on the original, with sharper points at the corners
-The knobs sticking out of the sides of the head (ears?) don't seem to protrude more at the bottom on the original--they seem to go more or less straight up and down
-Parts of the neck structure at the throat seem like they might be a little different, but it's hard to see due to the lighting on your renders
-Original model seems to have more protrusion of the upper lip, and less of an outward bulge in the area directly above that (where a human's nose would be)