Did a tour from a Carnival Ship (The Cool Runnings Party Boat) to the Falls... I was with 10 other people and every one of us LOVED the falls... They are about 650 or more feet high, and they actually are falls! Some of us are quite unathletic but it wasn't a bad trip up, and its like a natural high once you make it to the top.
We are going to Montego Bay this year on our cruise because we enjoyed Jamaica so much last year. I would say if you have the opporunity to go for it, definetly climb the falls. It's an experience you won't forget!!