I can't play FPS games on consoles for the life of me. I hate it. I need a mouse to be able to aim. The controller is retarded.
But i might get it for the PC. I am still occupied playing Team Fortress 2. Awesome game.
It's just practice. The 360 controller is somewhat deisgned for FPS (with the success of Halo).
I personally wouldnt play on a PC anymore, its just too boring and dare I say it geeky, and Ive been playing FPSs since Wolf 3D, on PC. Halo really changed that for me, and COD4 has cemented it, its amazing, and I can play it on the big screen with surround sound on a comfy couch online with 0 lag, 0 driver hassles, 0 PC related errors. It just works, and it works well, and it's fun.
Not to hate on PCs, last FPS on PC I played was Half Life 2, and it owned believe me. But Live on the 360 just suits my lifestyle more.