MTDEW,
same thing here. I actually found my self doing jump strafes and shooting at the same time, adjusting my aim in the air. That's no biggie w/a mouse and kb, of course, but I would never imagine that I could become that good with a controller!
So far, I'm on level 6 out of 10 (I think), trying to find Captain Keyes.
PC FPS games are definitely different from console ones. If you could play X-Box Halo w/ a mouse and keyboard with no modifications, it would be a lot easier, because of how fast (or I guess quick) you could aim and move.