I think the soundtrack along with the challenging boss fights was the main appeal for me.

18+ is not just porn. There is other content with adult themes being lumped in with it. Which is likely the actual goal. To suppress content that would lead someone to form an opinion opposed to their agenda.

Somewhere on the other side the universe an ancient being is devouring countless worlds to fill it’s stomach. How many orbs were taken? It does not remember. All it knows is the growing hunger as the orbs continue to take more and more each day.

It’s not only nostalgia. Arbitrary limitations drive creativity. Previously the limitations were imposed by the hardware. Today the designer can choose their own limitations.