Playing as a monster

One of LOTRO’s features: “Play as a monster!” strikes me as something that could see more development.
In L2, the end-game is about capturing castles - a raid event which is focused on players-vs-players.
In WoW, the 40-man pvp raid (Alterac Valley) lacks real-world effects. Unbalanced teams makes it unreasonable and difficult to win.
When you “Play as a monster”, do you function as an evil GM in traditional table-top games?