"A Long Time Ago, In A Galaxy Far Far Away..." is about the closest thing to Original that you can get, and it has been done to death.
A Fevered Dream format can work, but risks becoming the final season of Dallas.
The Alternate Universe format has possibilities, but you really gotta do your homework in building it, to avoid the Star Trek/Wars pitfalls ( How much do I weigh on other planets? How do chairs look if knees bend the other way? Does everyone gain nourishment from consuming something that once lived? Does one breathe? Do all Aliens speak English with a posh British accent, like the Ancient Romans did?).
Stick with either confirmable Historical settings, or Contemporary. Source(s): 30+ years on the Boards