Let's start with the equipment. There are things about them that aren't obvious just seeing them on the water. You start by putting on a skirt - think of it as a very tight girdle with a skirt attached. You then shove your legs into the front half of the hard shell that is the boat. That needs to be tight enough you can brace your knees against the side of the kayak, as you use that to control the roll on the boat. The skirt then seals around the cockpit that you're sitting in. This means you can roll the thing over without getting water inside the shell - which means you can recover by rolling back over, without having to empty the boat.
After some juggling, they found a kayak I could fit in. So I spent the first day in calm, flat water. If you've ever been rafting on the South Fork of the American river, there's a good chance you either put in or took out at Camp Lotus. The pond there is where I spent the entire day. The point was to become comfortable with the boat, to feel stable in it, and to learn the paddle techniques use to maneuver the boat. Oh yeah - I also had to learn at least one method of rolling back over if I got upside down. Since being upside down means you can't get your face above water without help, this is an important skill.
During the course of the day, my toes started going numb, as well as the insides of my thighs. This is apparently not uncommon - extended periods with your legs in a confining space seems to have something to do with it. Towards the end of the day, I started getting nauseous as well, so things slowed down. Given that, I decided that I'd use an inflatable the next day, instead of getting back in the shell. Thirty minutes after getting out of the boat, I realized that the feeling was coming back to my toes - which reinforced that decision.
An inflatable kayak is basically a one-person raft, with roughly the same cross-section as a kayak. You don't put it on - you sit inside it. It appears to be possible to treat it like a canoe, but I never did that. The instructors liked my doing this as well. I was the only first-time student, they felt that I would be ok with the intermediate class in the safer boat. So I joined that class, bringing it up to three people. One thing became immediately obvious sitting in the inflatable. Surrounded by all these people in sleek hard-shell kayaks, I felt like I was wearing a dunce cap. Oh well - the point was to have fun. Later, this got reinforced as the guide structured and paced things to the more advanced students.
This class did a slightly more dangerous stretch of water than beginners would normally get during the second day. It was downstream from Camp Lotus to the lunch spot that All-Outdoors used below Camp Lotus. There were no Class III rapids, but that was fine with me.
For those who have been rafting before, the position is different - instead of sitting on a tube with my feet in the boat, I was sitting on the bottom, with my legs stretched out in front of me. Like a hard shell, I still needed to be able to brace my legs against the sides in order to control the boat. The other difference became obvious the first time I went through white water. In a raft, the thoughts are that I want to hang on, listen for the guide, and enjoy the ride. In the kayak - there was no guide. I had to choose a line through the rapid, and decide what to do to get the boat going where I needed it to go.
I went through some rather nasty Class II's ok. I got to surf a bit. I bounced off a couple of rocks, and wound up doing the second half the rapids backwards. All just part of the ride - in an inflatable. In a hard-shell kayak, those would have been rather nasty. In the worst case, I wind up getting out of the boat in the middle of a rapid - on purpose!
One of the rocks I hit I didn't bounce of off - I stuck to it. It looked like the boat wrapped. It felt like the boat wrapped. However, the guide walked upriver to me, had me get out of the boat and stand downstream of the rock, and we pulled the raft off the rock. So this was technically a perch. Watching - and feeling - the water holding the boat to the rock, and pushing against my leg standing downstream of the rock, all the warnings about walking in moving water and the power of the water became very real.
In summary, it was a lot of fun. It was a serious workout - I was so sore Monday morning that getting out of bed was a significant effort. I'll probably do it again next season - and may well buy an inflatable of my own.