Consider this. For 2D action games you have high-octane surgical-precision gauntlets like Ninja Gaiden and Ninja Spirit, metroidvanias, platformers, and Apogee-esque explorathons like Commander Keen and Jill of the Jungle. There's plenty to find within each subgenre.
Meanwhile, for first-person shooters you have Apogee-esque explorathons like Doom (and its clones), tactical games, military corridor shooters, some first-person platformers, a whole heap of other stuff, but next to no high-octane surgical-precision arcade action gauntlets of the likes of Ninja Gaiden, Alien Soldier, Ninja Spirit, Contra, and so on. When people think of good action-heavy first-person shooters, they can only think of Doom (clones), which is very Western in design. However, to my knowledge there exists no first-person shooting equivalent to the Japanese arcade gauntlets of yore (because nips rarely ever touched this genre with a ten foot pole unless specifically catering to the gaijin audience). The closest equivalent would be Vanquish, a game different from its peers by virtue of its defined skill ceiling in singleplayer and high amount of techs.
Not counting rail shooters, is there no first-person shooter where switching weapons is tantamount to switching styles in DMC? Is there no first-person shooter which encourages you to play for score? Is there no first-person shooter with actually good boss fights at the end of each stage? Is there no first-person shooter which completely forgoes exploration in favor of traversing a clear and linear path and killing all the enemies on it as fast as possible? Is there no first-person shooter structured like an arcade game with limited lives, a total run time of 20-50 minutes, but high replayability? Or is this a completely unexplored region in the genre, and somebody has yet to seriously try their hand here?