One game comes to mind that I think would fit very well with Game Dungeon is Hellgate: London.
It was created as an early try at a FPS Diablo (made by ex-Blizzard employees) and it succeeded wonderfully in many respects and failed horribly in others, resulting in the company going bankrupt pretty early. Servers are down so none of the online play or additional expansion content is available but the original game can still be played in single player.