Okay, it's late and I'm tired so I'm going to respond to this more fully tomorrow, but after reading the rest of the responses, here are just a few comments:
1. This is NOT like your typical cruise. No formal nights...no boozers sucking 'em down at the bar...barely a casino at all (a couple blackjack tables).
2. You spend far more time on the islands than you do on the ship. It's more like a floating luxury hotel, traveling at night while you sleep so you get to visit more islands than you would otherwise, and you don't have to worry about making travel arrangements, or packing/unpacking.
3. The diving is UNBELIEVABLE! The crew is fantastic. You go in small groups in zodiacs right off the drop-down sports platform off the back of the ship. They do get a lot of beginners and resort divers, but they can tell when they get a diver who knows what they are doing, and they treat you accordingly. No herding, no cattleboats.
4. The price is amazingly reasonable compared to what you would pay for a land-based trip. The fact is that French Polynesia is incredibly expensive, rediculously so. Visiting it on the PG is one of the MOST cost-effective ways to do it.
5. The food is incredible...the service is top-notch. Crowd varies widely in age, depending on the length of the cruise. Shorter cruises (7 days) will have many younger people, especially honeymooners (it IS one of the most romantic places on earth!). Longer cruises will have more older, affluent people. I'm in my mid-forties, went with my Mom on an 11-day cruise...met up with several other people my age who happened to be there with their moms too, so we all hung out together and had an amazing time.
I have lots more to say, but I'll leave you tonight with this: I've been on numerous cruise, and traveled all over the world on land-based trip...this was one of my favorite vacations of all time. DO IT!