Morrowind would be something anyone would agree with. But besides that, I would have to say Disagea and KH 358/2 days. Disagea is self explanatory, but 358, despite the short hours of play it would take, somehow puts you in a world of which time just slows down. So from harvesting hearts and re-coning areas, what may of been in reality being a few minutes felt more like hours. Besides, considering the customization and challenges given to you, time is wasted withing good reason.