we went on this excursion on our cruise last week. went with my wife, 5yo, and 3yo. the aquarium was okay, it was all a bit chaotic in there with a lot of schoolchildren on field trips.
it was pretty small and they drop you off at first to watch someone feed and 'hug' the sharks in the big tank and then send you off to see the sea lion show. the show was in spanish, which was fine, our tour guide tried translating real time but it was too noisy. do NOT sit in the front several rows as you WILL get wet. the sea lion makes sure of it. you are then directed around to feed stingrays shrimp and fish, feeding some tilapia, we got to see a snake up close, and then around the zoo area. we had another 15-20 minutes to see the rest of the aquarium and then back on the bus to head to the beach.
we were driven for about another 20-30 minutes to el cid marina, where they had a fairly decent buffet lunch with free drinks, and then you could go to either the beach or the resort's pool. the beach was fine, it wasn't too hard to find a lounger, they gave you towels, and the waves weren't too bad for my children. a lot of vendors kept bugging my wife, not pushy but just kept waking her up.
it wasn't the 'best' tour, but the 5yo and 3yo were free and it was a busy generally fun 'family' day so i'd call it a success. if you don't have children i wouldn't recommend the tour as the aquarium part was kind of lame for adults. of course when i asked my children their favorite part of the tour, my son invariable said 'THE BUS!' /facepalm