Networked, team-based, gunfights in a randomly generated dungeon. Take a modern top-down shooter and toss it in a pot with rougelike dungeon generation, traps, and ridiculous characters and items. Welcome to dunGeon.
The mapmaker class can chart out the dungeon, and see where he and his teammates are on the map. As long as there is at least one mapmaker on the team, his/her entire team can see the map