I had a conversation with a friend a while back about art, and he was saying that it was hard to be original, because everything has been done already. I agreed, but it didn't phase me because I am not aiming to be original. Instead I hope to be genuine, skilled, straight forward, interesting, unique and other similar things.
Originally and uniqueness are not exactly the same. Everything but the super cliche is unique, when viewed from the right perspective. So if I make something, because I made it at the current time with my own hands, even if it has been done a thousand times, is unique to that moment, and so forth.
Is it original to paint a portrait or write a love poem? Not really. They can be wonderful, important expressions of a moment though. Records of human lives, and so forth. Unique expressions.
How does this relate to game design?
Can you make an original war game? An original dungeon crawler? Probably not. Can you make an interesting one? Yes. A well made one? Yes. Can you put a new twist on an old idea? Yes. And so on.
I'm not saying that no one does anything original, because sometimes you do stumble on something new. I'm just saying that if your goal is originality, you may encounter more frustration and stagnation along the way. Giving up the idea of original for interesting and unique has let me produce so many more things over the years.
I think if I was to make something original, it would not only be on the backs of all that has gone before in the world, but also on the back of all my creative work as well.
More articles on game design: Don't be Perfect!, and Don't confuse good design with your preferred style of play.