I grew up on consoles, mostly Playstations, so I can use controllers a lot better then some people. I prefer to use them in FPS', movement and melee feels a lot more natural with a controller then with a keyboard. Aiming is, I dare say, an art-form with a controller and it can get really difficult when the sticks are old and losing their sensitivity (*or it's just a crap controller).

Not to mention how comfortable it is not having to have your fingers splayed across a flat surface for the whole game.