First and foremost: excellent pose and apish look!
IMHO it only doesn´t particularly look like a gorilla. Regarding the face it may be due to the small nostrils, big ears, prominent cheekbones and the hair growing off them. To me it looks more like a macaque or something. The bulkiness in a gorillas' face would rather come from a wide lower jaw/chin line.
Also the overall look is a bit slender, but since it appears you intended to depict an older character this would fit well.
However, pretty impressive display of skill again!
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