Yep. I agree. K.I.S.S. is imperative to a proper FPS. However, there are things that can be done to make one FPS different from another. Otherwise, why create a new one? We can all just play Doom and Unreal over and over again.

One of the things I mentioned that I like about the old FPS is the discovery of what is going on. The story might have been there (Unreal) or not (Doom) but it was not the overriding thing that dominated the game (Quake 4). Discovery in Doom was the new weapons, the new opponents and the new environments. That would be a bit "thin" these days. In Unreal they had all of that, but they added some other things to make it interesting without detracting from the game play. Half-Life expanded the story aspect, but still somehow preserved the game play. It's when the story took over and controlled the player that I see the FPS decaying.

So, in the spirit of K.I.S.S. how does one preserve the spirit of the original FPS, but also provide something "new"?