Thats pretty hard to imagine. You mean one that has a deep, immersing storyline and meaningful characters who you can fully sympathise with but which still allows you to go bats-in-the-belfry crazy and do anything you please, be it building a massive empire or burning every last building and/or NPC to a flaming heap of ash?
If I come up with a way of visualising that... I certainly won't tell anyone, instead I'll be busy learning how to make computer games and making a fortune out of my idea when I release it.