You got the inspirations pretty much right. Quake 2 (my first FPS ever), DUSK, some Half-Life, Painkiller. Shotgun's horizontal spread was chosen just because Doom's pump shotgun also acts that way. There isn't that much vertical combat currently so a horizontal spread just felt more logical for me. Also, your post just solidifies more and more those things that I gotta fix/add to my game. I've gotten a lot of feedback and mouse sensitivity, scroll wheel weapon switches, and better HUD are high on the priority list!