The underground labs were genius. The very first one with the poltergeists... I've never experienced anything like it. On my first playthrough, I never realized that the objects flying around were caused by creatures that were killable. I raced frantically through the whole thing dodging random objects flying at me and wondering what the hell these big electrical clouds were roaming around. It was just such a unique experience with such an immersive presentation. It took a long time to get jaded enough to those environments that I didn't feel any real apprehension about going into them.
Those freaking labs. The floating objects were more an inconvenience, but any anomaly that I came across, I made sure to take extra caution around, just in case they could be messed around with by poltergeists, and then facing those apparitions, after killing one, a swarm of them came along, and got me into a shooting frenzy, emptying one gun, switching to another, until I was down to my sidearm to take them down, of course, until I had to reload them all after finding cover, where I'm still getting beaned by cans and bricks randomly, with the occasional heavy object that knocks me down.
It wasn't until the flying stuff stopped that I knew I got them all. What sucked about the labs and sewers worst for me had to be when there are bloodsuckers and snorks when you least expect them, and especially when you first encounter them.
My best first experience with the controller had to be when I was clearing out an area of bloodsuckers (open season) and as I was down to my last 1 or 2 bloodsuckers, my screen starts acting up and I hear a high pitched whine, and then I see this crazy-ass face pointing at me like a body snatcher. Unfortunately for it, it revealed it's position to me, and I killed it in 2 shots (at a rather significant distance, both headshots), and finished off the remaining bloodsuckers and then investigated what the hell I just experienced, and shot it a few more times to be safe. In a sense, it was one of my cooler experiences in that game as well.