Its a crowded genre with a lot of really good developers where even quality games in well known series have difficulty selling well ... With that said, I think it would be interesting for Nintendo to make a FPS that "broke all the rules"
Essentially, I think there is a market for the "Mario Kart of FPS" and by that I mean an arcade shooter that is easy to pick up and is not so focused on graphic violence, and is far more focused on being accessable. You could use the advance wars graphic style, and base the gameplay on Quake 3 or Unreal Tournament and make something that stands apart from what most other developers are doing with the genre.







