Basically an instance based game where you gather a team of dungeon delvers to explore a dungeon and get good loot. You would have to pick your loadout (equipment and skills) according to what you think would be needed to dungeoneer successfully for the given challenges of a dungeon. On death you would lose all the equipment you brought, but you wouldn't lose your level or skills.
Dungeons would have different challenges. So one might be a close quarters crypt like some Mayan or Egyptian pyramid. One might be a larger ancient city like Atlantis. Some a mix of both. The NPC enemies, traps, and puzzles could be random each time based on a pool of the types for those dungeons.
There would be other groups of competing adventurers trying to get through the dungeon, but I think the dungeons should be scaled so that running into them is less likely than say the game "Escape from Tarkov". Also I think the game should do a dice roll while match making to determine whether a given match has no opposing teams or many opposing teams. This will keep you on your feet PvP wise but allow the game to focus mostly PvE. PvP here mostly serves the purpose of providing a challenge to players that can't be "solved" since the ingenuity and unpredictability of players is greater than that of typical AI.