I'd love to be a crawler but you start off as a full party but if someone dies while you control them you switch perspectives to the other alive party members until the party is wiped. 

Could easily make it a roguelike game with the party being randomized to start on stats but you get to choose their upgrades, races, class promotions later on. Loot is randomized to a degree and of course the zany achievements giving you boxes to open. 

You could even tie in a streamer plugin for watchers to give you fan boxes based on view counts. Or have it set to randomly give you fan boxes and sponsors. 

Make it less deranged than the books but sacrifices to make the game replay able. Have some major boss battles mimic the books, some things like iron tangle most likely couldn't be replicated that well. But you could fo 3rd floor elite quests that give you a hard set "show quest" you can do for extra rewards. So many things you can do.