My last 3 cruises have been amazing!
My teenaged DDs enjoy alot of freedom on the cruise. Each time, I have sailed, there is one night where they come home later than curfew and I have to go out and look for them. After I "ground" them the following night, I have no further problems. Your children will act the way they act at home. There may be a few "wilder" kids onboard but they are few and far between. Just arrange check-ins with them and make them stick to them.
What has really been cool for my girls is the friends they've met on the ship from all over the country. They continue to IM them, months after the cruise. One guy took my daughter to the Fall dance. (He drove up from an hour away - he was a really nice kid.)
These cruises are really expensive! There is no way I would keep coming if we weren't having a blast!!