The purpose behind creating Bitcoin Gold was to make mining decentralized again.
Satoshi Nakamoto’s idealistic vision of “one CPU one vote” for Bitcoin had been displaced by a reality where the manufacture and distribution of specialized mining equipment using ASIC (Application Specific Integrated Circuits) chips is dominated by a tiny number of entities, some of which have engaged in monopolistic and arguably abusive practices against individual miners and the Bitcoin network as a whole. Changing the PoW (Proof-of-Work) algorithm from SHA-256 to Equihash means that specialized ASIC mining equipment designed for SHA-256 are unable to mine on the Bitcoin Gold blockchain. Equihash runs on commodity graphics cards, or GPUs, which are easily available to the public, but Equihash is prohibitively difficult to implement as an ASIC (see: Equihash). As a result, Bitcoin Gold provides an opportunity for countless people around the world to participate in the mining process with widely-available consumer hardware that is manufactured and distributed by reputable mainstream corporations.
This leads to a more decentralized, democratic mining infrastructure that is both more resilient and more in line with Satoshi’s original vision. Bitcoin Gold was created with that vision in mind. This, to me is the uniqueness of bitcoin gold.