I used to hate the idea of controlling an fps with a pad, but its really pretty good once you're used to it, and like Ad said, with a DS3 and real triggers its the business
I have mine set to High sensitivity, and its pretty controllable but the big difference compared to kb/mouse is if someone surprises you swinging round onto exactly the right spot is no easy task... with a mouse you can just swing round and shoot in milliseconds but its a fair bit slower process with a pad... but hey, everyones in the same boat so its all fair