I gave Dive Quest to my dad for his 70th birthday *gasp* five years ago. My stepmother went with him. Both are very veteran divers. It's fantastic.
You will get a controlled dive for about 25 minutes and then let loose with a dive buddy for another 25 minutes. Don't worry about the sharks. They just swim by you. My dad and stepmother have dived all over the world and they keep talking about how great the Disney experience was. If you have family with you, make sure they are in the viewing area. They will be able to be featured on the dive video. And make sure you get the video. It's a great way to re-live the experience.
The people in the normal viewing area really get a kick out of seeing the divers in the water. We were there just watching and when the guests realized we were tracking my dad and stepmother, actually treated us like royalty because we knew people in the water. I think I had more fun than the divers!
One note - if you do have family and they will be meeting you after the dive, don't follow the recommendation of having them wait for you in the gift shop. We waited for well over a half hour because of the after dive debriefing. Make plans to meet somewhere else in a certain time frame. Frees up your family quite a bit after the dive is over.
Oh - and save your receipt. You can write it off on your taxes since all proceeds go to animal research and it's a charitable cause.