These party snorkeling catamarans have their virtues for the experienced snorkeler.
It was a beautiful day, and we sailed out to a reef in the Gulf (at least, that's where I think it was). Upon arrival, we were instructed to avoid certain parts of the dive area, and where to go for the best snorkeling. Unfortunately, after going under water for the first time, I more or less lost my bearings and wasn't really sure where I could or could not go. This, unfortunately, detracted from what I was able to do.
Now, I had snorkeled two days prior so I knew what I was doing and am a strong swimmer. Since you are out in the open ocean, however, it wasn't unusual for a wave, however small, to crash over you as you breathed in, resulting in a lungful of ocean. For that reason, if you've NEVER snorkeled before, don't make this your initiation.
The good was that we got to see quite a few huge eels, fish (barracudas! don't wear a watch!) and all sorts of sea creatures if you were brave enough (and could withstand the pressure) for a 20 foot descent. Some folks even reported seeing some small sharks.
On the way back, they broke out the beer and wine, we watched the sun set, and folks partied till we got back. I must admit, though, I was so tired after 45 minutes snorkeling - all I wanted to do was sleep.
If you're an accomplished water sportsman, it's fun. Novices, not so much. Also a bit of a singles scene if you're into it.