I say make it like KOTOR game mechanics (without the name) except where you can be many different species with different occupations and have different places with different time periods, give it an open ending with no replication of already made characters (no luke skywalkers, darth revans, etc.) and uh, make it free.
Yes I know I'm dreaming. (sigh) why couldn't God have given me his powers for Earth only? But then again, I sure wouldn't want a game if I had those powers...