Valhalla (and sequels) gets adapted into video game form. What genre of game is it? Which characters are playable? Does it have any notable changes from the plot of the books?

I’d not try to adapt the books, I’d try for an mmorpg where you can just live in that world. Be on a team, or be a villain of your own design, or just explore ala Breath of the Wild. Tikari themed mini-games abound.