Good FPS for an old guy?

Hi, I don't often play FPS games but am looking for something to kill time with. Everything I've checked out (Titanfall, Doom, Halo 5, etc) just looks so similar. Are there any less frantic/colorful ones comparable to Gears of War out there? I could almost play GOW1 forever but it's finally starting to bore me. But mechanics wise, and visually, that's more my speed. Thanks!