There are plenty of non-serious FPS games being made that aren't COD like. Shadow Warrior, Serious Sam 3, Painkiller Hell and Damnation (even if it is a fairly meh remake of the original), Rise of the Triad Remake (even if I don't like it much), etc and so forth. That style of gameplay is far from dead. There's a Serious Sam 4 in the works too last I heard. The audience is out there and so are the games. Just gotta dig a little bit beyond the surface level.
By the way, Descent Underground made its Kickstarter goal. Congrats to those lucky guys.