Good idea, I can't believe I haven't seen an FPS endless runner before. The shooting mechanics are a little frustrating at long range though, since the bullets shoot from gun barrel direction and not the direction the reticle aiming at. To fix this in my game I attached a script to the projectile that initially launched it from the direction/position of the gun barrel, but over the course of a half second moves it to the in front of the reticles screen position and direction. This still gives the effect of the projectile moving from the gun, but makes it more accurate. Very nice game.