The rock climbing wall is usually well used by passengers. The "routes" up the rock vary in difficulty and can be changed, although I don't know how frequently they are changed. Some of the routes are easy (as far as rock climbing goes), and some are difficult in that you are beyond vertical at times with your back to the ground. I had never rock climbed before this trip, but I absolutely loved it.
I too agree they could keep it open longer, but it takes quite a staff for it. They need at least 1 crewman/climber, and then 1 or 2 other people mannng the signup sheet and getting folks into the gear. If you are interested in this, go there as soon as they open on the first day and at least get the waiver form. I've been on ships where they've run out of waivers and have to wait for more to be printed. This way you'll have it already to go when you are ready to climb.