Oni was a revelation for me when I first played it. It offered the nuanced melee combat of classic fighting games in well-realised 3D plus precise third-person gunplay that improved on the most exciting parts of Tomb Raider, all in the context of a crime thriller where player decisions made a difference to how events played out.
What little knowledge of anime I had when Oni was released came from Akira and Gatchaman, so that aspect of the game wasn't as important to me, but Bungie did a great job of creating an authentic corporate dystopia filled with fractious relationships. Railing against those challenges is Konoko, a likeable protagonist with a real personality.
Oni is just an under-appreciated gem. I've voted for several Good Old Games to be preserved, but if I had to choose just one for the GOG treatment, Oni is the one I'd like fellow gamers to experience.