It's definitely worth a visit at least once.

(Note: in summer, it can get very muggy and hot there. Keep in mind, there's a walking tour for part of it--spectacular views. I think it's more enjoyable to walk in cooler weather, but that's just me.)
Read recently that in 2012, they added more attractions; it used to be just the walking tour and then the guided ride with a group on the 32-foot bateau down the gorge--really fun--and I'm happy that I experienced those original bateau rides. Now, they still have the original walking tour, but also have tubing, rafting, hiking and a high-adventure course with rappelling and cables.
Here's one the best descriptive reviews I've read on the net:
http://www.ohio.com/lifestyle/downi...fers-beauty-nature-history-adventure-1.627072