Sandbox multiplayer - DM or coop rules are undefined. Players individually can choose to team up against other players or against monsters, or go it alone. The map would be interconnected while maintaining a progression through monsters, traps, and puzzles to the exit.
I guess this would be close to coop with friendly-fire on, with a little more acknowledgement of how frequently casual coop players turn against each other.
End of level should show more stats per player and players can decide on frags, monster kills, or speed through the map counts the most
Should the exit end the level?