Rip, I think you are doing very good (manual activity, participation, WTG), but I guess you can relax a bit the rule, as a lot of posters said, you can permit the Devil to enter your house but with a firm time limit and an "approval veto" by you on the game.
Dont let them play too much and with wrong games, chose always games that force the use of the brain, or that simulate the physics of the real world (aka the sims).
About the RPG games, I dont understand why you oppose, there's a lot of good stuff around, with a complex interaction and a deep "parallel reality".
Just for a try, give a look to "Morrowind", I am exploring it now, and make my jaw fall everytime I realize the number of quests, the good complexity of the social structure, and the cure in creating the world. (Every house have his own objects distribution and a large variety of structures).
Moderation it's the key.