Ok, let me first say that I'm not a game developer so I have no intention of doing this game.  (Although I'd love to BE a game DESIGNER- and be able to spell without spellcheck). 

So basicaly the game is, your a Litch, for those of you who don't know what that is it's an undead wizard (ususaly). 

The begining of the game, and maybe the most important part, is choosing how you became a litch.  Now this can be a game in and of itself or just choosing a series of options.  Say you're a wizard, etc, who cast the spell for whatever reason so you can live for ever (well until destroyed anyway) or a warrior who had the spell cast on you, or an item, etc. 

Then you choose how old you were when you were turned, and what you looked like before the spell/death (There'd be an illusion spell so you could look like this again, and go about biz in normal cities).  You also choose how long you've been undead, which is important for starting skills, items, and home.  Say between 50-1000 years.

The whole point of the game is to die, but only when you're bored with the huge open world.  The choosing of your power level pre-game, the age, stats, etc, is just to make the game more or less challenging with how hard it is to do whatever it is you choose to do.  And at death it would tell you how you affected history, etc.

Now you could choose to do anything in the open world.  Regular fantasy, middle magic (That is, magic isn't rare but is very hard to do, making magic very powerful-sort of like a channeler but a little lower) realm with all sorts of creatures, possible quests, etc.  A living world with different nations, and nations of people.  Trade, science and technolgoy and magic RESEARCH - (Because you could live another 1,000 years and see the world slowly change).  You could also go up a meta-level and partake in the strategic level of the maps by conquering a nation, being elected to an office, becoming a baron, duke, whatever.  And there of course you'd be able to do all sorts of interesting things. 

Anyway, I get interesting ideas like this all the time, but I think it'd probably take more than a few million $ to do correctly, or someone much more talented than myself to create even a low graphical version.  Anyway, at work just letting a little creative juice flow.