If they like fighting games and RPG types, Too Human is pretty sweet. I got it a last Saturday, and I have been playing it a lot. It's got the sort of Diablo dungeon crawler feel (or so I have been told - Diablo came out before I played PC games at all). Think Devil May Cry, but with a little less over the top action, and with a huge RPG loot gathering system. It's based on Norse mythology, but with high-tech sci fi added. It's rated T too, so it should be ok.