Take, for example, a Soul Eater RP I'm working on and playing in. Granted, Soul Eater is not as often done as many other fandoms, but it is still set in the world and has a somewhat similar story to the base work. But the entirety of the cast is full of original characters and set in more of an Alternate Universe. The characters are deep and complex, each one having to deal with something different about them selves as well as personal growth, but the story line itself follows the same idea as the base work, only in it's own and different way.
On the topic of creativity and originality, nothing can be imagined from nothing, you can not create in a vacuum. Everything is inspired from something else. I spent the last three days writing up an entirely new religious sect for a D&D game, and after all was said and done, I found it reminded me greatly of the Justice System from Judge Dredd, but was still it's own even so. I'm writing a character background for another one, a classic disgraced noble turned rogue, but with a twist of my own tossed in. Even such things as what I defined as fandoms have a degree of originality. Original does not mean 'never done before', this is a misconception, it means 'new'. A new story, a character, a place, a power, just adding or twisting something from the base work makes it new to it, thus, original. Again, take my example of a Soul Eater RP. From this prospective, other than the setting and some lore, the RP is, in fact, almost wholly original.
But this is all a matter of opinion, what one person thinks is original, another may think is not or over done, no matter how many twist or changes are made.