My brother (with CF) has been before and LOVED it. The health factor never even crossed it mind! He promised he'd take me for my 18th birthday.... well that didn't happen, then again for my 21st, again, no dice. I've always wanted to go and WILL someday.
I have been Scuba diving though and had no problems, it actually was a lot easier for me than most because I'm so in-tune with my body and sinuses that changing pressure was much easier for me that experienced divers, I'm able to sense and clear ear/sinus pressure with almost no thought. I did start coughing slightly when I hit about 35ft, but all I had to do was clear my breathing regulator and I was good to go!