Hello. I have parasailed several times. I think it is a blast. You can definately bring a camera. If you want, you can ask if they will "dip you" in the water. They slow down and let you fall into the water for a "dip", then they speed back up, and back up into the air you go.
It's a blast. As far as booking directly, I would assume its cheaper finding something on your own. If I remember, last I saw on RCCL website they wanted $75 for a parasail booked through them. That is more expensive, but saves you the hassle of spending the time, of trying to book it on your own. Several times in Mexico, I have walked up to the parasailers on the beach and gotten a ride for $20-25 bucks. I just had to wait my turn. Hope this helps, Lil' Lori