Now that i think about it its pretty hard to think about things that have never been done. Just like movies--for example zombie movies and games. There are so many and yes they are usually good as games. New spin offs are always good to see.

One game I thought was semi-original was defiantly Okami. The art style i've never seen before, storyline and character.

When I think about having a villain it reminds me of Fable because you can make your character evil heh heh. Hmm...I really liked dinosaur hunter that was fun. Just like one of the original dinosaur hunting games(no one seems to have heard of it) called Carnivore for the PC.
As for unicorn games that has already been done with Robot Unicorn Attack which is fabulous and addicting. Even made a death metal version. This is all on adultswim.com though.