We did the Blue Lagoon excursion last year and we had a great time. There have been many opinions on this, many like it and many don't. As first time snorkelers, we had a very nice time. There was not a ton of fish, but we were easily impressed. The beach was very clean. I have heard others think it was not. If you have little ones its great because the cove is very shallow. Lunch is included. It is your typical bbq, the punch was horrible so bring something with you. We stayed until the first trip back at 2:00. You can also go back at 4:00. The boat ride was nice but a little long-about 30-45 minutes.
Would I do it again, yes! In fact, we had planned on doing it again in June. My sister and her family are coming and they have never snorkeled. They have a ds-7. I thought this would be nice not knowing if they would enjoy snorkeling.
However, after reading up on the excursions, my sister wanted to do something else, the catamaran sail! I was pleased because we really wanted to try something different. There appear to be a few pluses (sp?) from what I've heard (I just asked about it last week and heard some very nice reviews). There is no lunch included, but others have said they were back and eating by about 1:00. I liked this because we didn't have a chance to have lunch on the ship last time. Also, it will give us a little more time for other things such as the spa or going for a quick visit to the market. I would like to say that I have done this as least once in my life. The earliest we got back and out and about was about 3:30 from the blue lagoon.
I'm excited for the new excursion but I certainly wouldn't have hesitated to do blue lagoon a second time. Have fun!!