It seems everyone has read the post in a different sense than I'd intended. I'm not suggesting that people pass copycat games off as originals. It just might be a good workout.

For example, a lot of the fun in DOOM has been (in my opinion) lost in later generations of FPS. An honest attempt at copying might have helped game designers capture the little details that made the game fun - not just the general idea of "whoo I'm a first-person shooter".